It probably gets worse after your eat because the baby is already pressing up toward your lungs and when you fill your stomach there is even less room in there
If carbs make it worse, I think that would make sense because they often take up more room. I am 24 weeks and already having this problem - I want to eat like a pig, but when I do I feel like I am going to explode and can't breathe well. This is my second pregnancy - with my first, at 8/9 months, I had to eat really small meals, because there was NO room - I would get bad hearburn and breathing trouble if I ate a big meal or even drank too much water at one time. Good Luck!