Had what believed patella tendonitis..cause of pain under knee...now it feels better but get occasional pain on side of knee...what is this?

Many possibilities: First, it depends which "side" you mean. There are many stabilizing structures in and around the knee. On the sides of the knee are collateral ligaments, one on the outside (lateral) and one on the inside (medial). There are two menisci, one each side. And there are tendons that cross the knee on both sides. Inflammation, overuse or injury to any of these structures could cause your pain.