Sex is fine unless your doctor tells you not to! Its completely healthy. And sleeping on your belly is fine as well until you start feeling uncomfortable. This is NY second baby and I've slept on my stomach quite a bit til i started getting big and uncomfortable
Sex is actually quite healthy during pregnancy and a good way of exercise, and the baby is well protected so yeah you can sleep on your stomach until it's uncomfortable
Girl women have sex up until labor!! So why not? And you can sleep on your belly until it's uncomfortable for you.