Baby fighting bottle - almost 4 months

AB

My bub turns four months on 22nd. I had to introduce formula about 15 days ago since I am going back to next. She takes one afternoon feeding of formula rest expressed breast milk using bottles. She is only drinking milk from bottle after she falls asleep or when she is about to wake up. Rest of the time she sucks on her thumb or pacifier even when she is hungry. Is anyone having same problem. Should i take her to doctor office?