it will be helpful if u explain little more abt how did u fall??on side or front?it s not necessary that you get knee pain only when u had a direct hit or blow..if u have twisted ur leg while falling, thr are max chances of ligament injury..while standing if ur tibia s pushing out in forward direction as you said it will be wise if u get it checked thoroughly.thr is probability of ACL strain or tear..did u take a complete rest and have you put any supporting pad while walking in these 2months??advice to you is dnt play wth a painful knee it may become worse.be careful while stepping down the stairs and start with ur thigh muscle strengthening.dnt worry much just be careful and get it examined as soon as possible.