Sounds like a growth spurt hon, if he is drinking and drinking then he is obviously hungry. Also as he gets bigger he needs to build up your supply. It will pass - just rest while you can and remember that he will settle back down again... for a while, then there'll be another one! But sounds like you're doing all the good things as he is gaining plenty of weight. It will pass... probably quite soon... in the meantime, rest and take care of you.