My boyfriend doesn't like ?

My boyfriend and I are 19 years old. Although we are young, we do have a 4 month old baby. As soon as our daughter was born, and I was all healed up from the delivery, we were crazy about eachother and ready and MORE then willing to make love. All of a sudden, I have found a very big decrease in his drive, and when we do have , it is HORRIBLE! I know thats awful to say, but at this point, he's a one pump chump, leaving me unsatisfied. I was just wondering if I could get a few inputs or suggestions on this situation I am in. It's driving me crazy, because I'm totally lacking pleasure.