it happens, in recent few days, on my son, 3.5months old, as well. he is very irritating on bottle feeding. we will take him to have doctor check tonight.
Don't worry, my son has got the same problem when he was five to six month old. everytime we can only feed him when he was sleepy. whenever he was awake, he refused to drink the milk.
There is no other way except to follow his will if you dont' want to force him. But rest assure that it will change when the baby grow older. When my son is about seven to eight month old, he drank his milk no matter he was sleepy or awake. I have asked the doctor and he said it was quite normal. baby like to explore more new things when he is awake than to drink milk which is too boring for him.
The doctor told us not to worry. when bb grows older, he got stronger interest with his surrounding environment. just dont disturb him, such as talking to him or turning on tv, when he is eating. as long as he keep growing along the curve, it is okay.