third trimester and sex

I'm currently 30 weeks, and I'm either sleeping, eating, or just feeling in the mood in general. My fiancé and I tried having sex about a week or two ago and it felt like I had shrunk or something. It felt impossible for him to get it in, and we didn't even get to do it. We still try to fool around some here and there but still. Anyone have any tips for sex positions or anything? It's driving me crazy!