@gabe7587 First, CONGRATS! This is an exciting and sometimes overwhelming time. Just remember that there are no rules and kids are little chaos engines. Listen to your instincts and feel free to ignore unsolicited advice - even mine!
As many others have pointed out, weight fluctuations can be completely normal. If he hasn't attended one yet, please have your husband attend your next doctor's appointment so he can talk to the doctor directly about his concerns. I'm a guy and understand that from time to time, we can be pretty clueless about the female body and need an "authoritative figure" to set us straight.
For what it's worth, my wife lost weight during her pregnancy with our first child. She gained a few pounds in later months when the baby's growth really accelerated, but after our oldest was born, she was immediately lighter than when she started the pregnancy. A lot of it came from dietary changes and eating better for the growing baby.
And finally, some advice my dad gave me on my wedding day: Your life will end three times - when you get married, when you buy a house, and when you have kids.
He was right, in his own way. The routines and "life" you had before those events essentially ends. Priorities change, new things become more important than old things, and that's okay. Just remember to take lots of pictures so that you can embarrass your child later in life. It's a parental prerogative after all...