MCL injury setbacks and long healing period

Patient background: I am age 61 and for 40 years have been a recreational runner/jogger. I have had a few injuries over the years - left knee meniscus, right hip stress reaction - but nothing in the right knee until now.

Injury Description: Seven months ago I was laying on my right side on the couch with a small pillow under the lateral side of my right knee. My wife was sitting next to my feet, and my right foot was tucked underneath her leg. I fell asleep while watching TV and then she stood up to get off the couch. So her leg pressed downwards with all her weight on on my right ankle and foot, and due to the elevated position of the knee, caused my lower leg to pivot at the knee joint towards the lateral side. A hot flash of pain woke me up suddenly, with very strong pain in the MCL region. I just rubbed the knee and relaxed, then went to bed without thinking much of it. However, a few days later I went to run, and started off with a mild cramp-like feeling in the MCL region. A mile later while jogging downhill I felt serious pain in the MCL region, but after stopping to walk to the bottom of the hill, I was able to very carefully jog the remainder of the run, but felt cramping/mild pain which got quite a bit worse the following day.

Post-Injury Treatment/Rehab: For the first month post-injury the MCL area was painful even when walking. I could not bend the knee more than about 15-20 degrees without sharp pain in the MCL region, especially when the knee was hanging free. I also had sharp pain whenever I happened to even slightly bend the knee laterally. So post-injury, I took one full month off with no running, and no exercise walking except to and from the car or getting around at the office. During month 2 and month 3 post-injury I walked an easy 2 miles once or twice a week, plus I did some gentle resistance exercises for MCL tears, pressing the outside of my foot against a fixed object and pushing outwards while sitting. I also did some gentle squat-style shallow knee bends - only 10% to 15% range of motion - a few times each day. During month 4 post-injury I jogged at a turtle's pace of 13-14 minutes/mile about twice a week (5 mile runs). During jogging there wasn't any pain as long as my running stride was controlled, straight forward, and on flat ground, and I made sure I did not run harder downhill and avoided uneven ground and any sudden turns or laterally forces. Generally, I found that I was pain-free during runs; however, occasionally for about 2 or 3 days after a run, especially during this early rehab period, I experienced stiffness and also some minor pain in the MCL region. During month 5 I ran more steadily (2X or 3X per week, 5 miles each run, at a very slow, steady jogging pace of 12.5 to 13.5 minutes/mile, and went on vacation hiking and swimming and managed to run 3X in one week without any setbacks. The frequency and severity of stiffness and pain afterwards seemed to be diminishing quite a bit. During month 6, I made my weekend run a bit longer - 6 to 6.5 miles, still at an easy pace. The longer weekend runs were more likely than the shorter runs to cause stiffness and MCL-region pain for about 2-3 days afterwards, but in every case the stiffness and pain went away by 3-4 days. Recently, during month 7 post-injury I decided to try and get back to my previous average distance from last year, and last weekend I ran 7.75 miles on a day when my knee was feeling particularly strong. I had no pain at all during the run (which was still at a slow pace of 12.5 minutes/mile). However, the next day the stiffness started in the morning and by later in the day I was in serious pain in the MCL region. It was a little painful to walk for 2 days, then eased up on the third day. On the fourth day the pain was gone and I jogged 6 miles, but during this run as well as the next day the knee was a bit stiff and slightly painful. At this point I realize I am not able to add mileage above a certain point, and I wonder if I might have set back my healing timeline by a couple months. I'm not sure why this injury has taken almost 8 months and I am still so easily re-injured.

My question is: Should I get an MRI - it would be quite expensive - or just cut back my rehab plan to where I was 2 months ago - 5 mile runs - and hope eventually this heals? I have talked to a sports therapist/personal trainer who told me to purchase some stretch cords to use for rehab exercises to strengthen the knee against lateral resistance. P.S. - I work in an office setting, very long hours, 12 hours per day, and drink 3-5 cups of coffee per day. I have been taking glucosamine and calcium for 16 years, and am lactose intolerant. To my knowledge I have no arthritis and have no previous history of injuries in the right knee. My goal is to get back to 20-24 miles per week which is what I did last year. Up until 5 years ago I was running 30 miles per week.