How To Make Your Shoulders More Flexible For Gymastics?

Okay So Im 13 A Girl I Barely Started Gymastics And My Shoulder Flexibility Isn't Great I Barely Started And Have Been Doing The Bridge I Am Kind Of Flexible cause I Did Use To Do Martial Arts And Also Umm Any Tips On Doing A Handstand? Because My Balance Isnt Great Either Well Its Okay And Is Your Head Hurting Normal After Gmastic Classes?