The bottom of my knee cap is hurting are these just growing pains?

Well the bottom of my knee cap is kinda hurting sometimes my mom who is a LVN said that it is growing pains I am 13, 5'3" and weigh around 125 lbs. I don't go outside but I work out in my house almost everyday (I think that I am to young to weight lift so I don't). This has been going on for about 2 or 3 months, the pain is not that bad and it is only in my left leg.