Hi Justin
You’re a smaller guy taking part in very physical activities your wrestling and getting hit in the chest will definitely cause the discomfort and being 90 lbs there would not be much padding so repeatedly getting hit can really hurt.
During puberty it is common for boys to experience nipple pain and tenderness.
It's called gynecomastia it's breast tissue built up from when a guy is going through puberty. It's caused by extra estrogen in the guys body.
So it could very well be just a combination of repeatedly getting hit in the chest area and going through puberty.
A bit of a break from wrestling may help and give the injured area a chance to heal I don’t think you have anything to worry about but if it will help put your mind at ease you may want to see your doctor just to make sure everything is okay.