Why does a 4 month old refuse bottle and breast milk

An

My 4 months old keeps in refusing bottle and breast milk. Its been a couple of weeks like that. She only feeds once she is falling asleep only when she is awake she keeps on refusing to feed.

Sometimes she can only finish 90 ml also within 1 hour little by little. She cannot finish the whole bottle at once.

What could be the reason? The drs says her weight gain is ok for the age but I think something is wrong thats why she is not feeding well