3 mon dd stopped drinking milk(since 1 week)last chechup was recent so she gained overall.used to drink 600-700ml now only 500 by forcing?

Normal Variant: 3 month old should be taken 150ml-200ml/kg/day of milk average. Sometimes there are periods when children eat more (growth spur) or less (sleep more for ex.). If the 3 month old is acting as usual, has no other symptom (fever, cough, runny nose, diarrhea, etc), is urinating normal (at least 3 wet diapers a day) then no worries. If not needs to be seen by his/hers pediatrician.

I'm concerned.: Young infants need approximately 150 ml/kg/day of fluids. I'm guessing your baby @ 3 mo. is ~5 kg. That means she needs 750 ml of fluid a day to avoid deydration. Milk is about 80% water, so 500 ml of milk provides about 400 ml of free water. This is just an estimate but it seems she isn't getting enough fluids, not to mention calories. Get with her doctor about this ASAP.