Baby not drinking milk

Ni2 ❤

Friends, my baby is 3 months old. She has been taking milk reguarly until last week. But now she is very busy sucking ner thumb and takes feed for just 2 to 3 minutes. She seems.to be happy and also have wet diapers. But whenever i try to feed her she is interested only in sucking her fingers and cries when i take it out.what could be the problem?