I have a three month old daughter also. She has four feeds a day (which they have told me is not enough, but she doesn't want a fifth feed) and has anywhere between 140mls-160mls a feed. She will probably drink about 30mls of water a day if it is hot also.
I have not started her on solids yet, and like your bub, she is awake all day, but she sleeps for like 10 hours (at least) a night, so i figure she probably doesn't need much sleep in the day. If she doesn't have at least a few 20 minute naps though, she does become upset. She is also very frustrated because she cannot move either, and i find she is happy if she is playing (mind you, i have to change her position and activity every half an hour and she is happy, i think they get bored). I have a Fisher Price Swing i put her in that has toys hanging off it, a bouncer, a Fisher Price Star Gym (she absolutely loves it!) an ocean wonders aquarium so she can play in her cot, rattles, cuddly toys and now she loves the Chrissie Tree too. Quite often she is happiest propped up in a pillow watching TV.
Just keep your bub busy, and she'll be less unhappy i'm sure of it smile