My labia is swollen pretty bad after sex but it doesn't hurt? We used lube and experienced no pain during sex either. What could it be?

A few things. Intercourse can cause swelling sometimes. Unless there is pain and bruising it is likely to resolve on its own. Yeast infections can cause redness, swelling and irritation. Monitor over the next few days and if it does not get better then consider seeing an Obgyn.