Idk what to do

My baby is 4 months old and is refusing my breast she just screams and screams ive gone to the dr to cheack for qny issues and all she said was maybr it just teething. As there wasnt any thrush or anything. Idk what do im so upset idk what happen to make her reject it and idk how to get her to go back im pump feeding atm but my supply has gone down alot. Has this happen to anyone els what can i do im so lost.