Hi Distancenewbie and thanks for posting and asking for some advice. I suppose we need to consider if the 'knot' is overlying the actual shinbone (tibia) or at least is emanating from the junction of the muscles in that area and the tibia. If so it could have been some calcification due to excessive pulling on the attachment to the bone. Mechanically the deeper calf muscle (the soleus) is the one most active during the impact phase of running. It is assisting to control/slow down the ankle movement when you land on the foot. If that movement is a little too fast or loaded such as with over pronation then the muscles on the front of the shin will also have to work overtime to slow down the inward roll across the arch. Problems with over-pronation or excessive supination can lead to injuries like shin splints, tenoperiostitis, tenosynovitis etc however as a runner you just need to look at the mechanics that are causing it.
If your skeletal structure is such that you do over pronate or excessively supinate then you can consider which footwear could be beneficial vs. which could exacerbate things. I suppose keeping it practical if you can go to a good runners shoe shop that takes a video of you running then you can discuss what they see and which running shows might be better to address that. Prevention is the name of the game as when things are painful they have usually been a long time in the making. They are never just what you did the day before, they are cumulative, overuse issues (sometimes related to poor diet as well due to poor recovery and repair).
If you can think about the cross training benefits of fell running, or cross-country training to wake up the whole lower limb musculature. Take a graded approach and monitor the symptoms in relation to training location, duration, rest. This will give you great insight into what's going well and what needs adjusting. Also some other leg activities like spin training or swimming would be useful in pumping blood around the legs as well as for your overall fitness as well as working the lower limbs in a different way.
I hope this gives you some new ideas on how to plan for progression. And as I like to say 'In the first six weeks your are training to train'. You don't being training on day one, your body is never ready for it.
Let us know how you get on.