It has nothing to do with your 7 lbs. But honestly, he might not have a very high sex drive - and if so, that might be a problem.
Does he call for phone sex after kids are asleep? How much does he call or text during the week?
This isn't a new thing - the sex has always been few and far between and somewhat dependent upon you making it happen. It might not be as important to him as it is to you. I wouldn't jump to that conclusion but I'd be watching for it.
And I think it would be fine to just say something to the effect that "sex once or twice a month really isn't enough for me".
