As long as your dr is ok with your weight gain, then I wouldn't worry about it. Your boyfriend is just being rude if he is calling you fat, because we all being to feel like beached whales at the end of our pregnancy no matter how thin you are to begin with. I personally looked bigger with all my boys than I did my girl. I hope the rest of your pregnancy goes well. And if he continues to give you hard time offer to make a mold of your belly and then lay it on him and see how he feels. Or better yet they do make those tummies for me to wear that actually put pressure on the bladder and make them feel what if feel to be pregnant. I hope this is encouraging.
Since you're so early along, it's nothing more than bloat right now. It'll go down over time (don't know how long. I was bloated for months before it stopped) and then you'll start to get your baby belly. Does your boyfriend mean it in a joking way, or is he being serious. If he's bothered now about it, then he'll go crazy when you start to get bigger and in more pain from the pressure of the baby. Remember that it's normal to gain weight, and it's something you need to do. If you're underweight, you'll want to gain even more. (Normal weight: 25-35 pounds, underweight: 28-45 pounds)
I'm sorry but I just did the math and you say your are due in april. how is that possible? Especially when it is only July 4th?
Wait... i sound stupid but really you must be extremely early and couldn't possible be showing and if that is seriously the case then you really need to tell your boyfriend to shut up.