E.L.
Hi J.. I am no expert on marital problems, but I am also pregnant. I am about 5 months pregnant with my third. Usually around this time, I am ultra sensitive to everything my husband does. I don't know if your husband is cheating or not and I don't think anybody here does, but I do think you should do three things. First, talk to your husband about it. He may blow you off or go into a rage regardless of whether your accusations are true or false, just out of self defense, so be careful in how you approach it. Maybe even write down some things you want to say so you don't get caught up in emotions during your conversation. Make sure you find a time to talk when you are alone and without distractions.
Second, make sure you really know what's going on with your finances. My husband gets really stingy about money when I'm pregnant, too, so I'm guessing that's just a natural thing men go through when their family is about to grow. It's stressful. And when you are the one responsible for the spending the household money, it can make you feel guilty for every little thing you buy from groceries to something new to cover your growing belly.
Third, I would seriously talk to you doctor at your next appointment about it. Your doctor can give you contacts and phone numbers for good counselors that will be covered by your insurance. Even if you husband refuses to go, you can. Not only will you hopefully get some good professional advice about your concerns, but it will show your husband that you are seriously concerned about your relationship and want to make it better.
Good luck with this. I really hope that it all turns out to be nothing and works out for your family.