Lump on vulva

So yesterday morning I woke up with a hard lump on the lower part of my left labia majora. It's about the size of a pea and it's painful. My boyfriend and I had sex the night before and I thought it might be a bartholin cyst but it doesn't seem to be in the right place. The only time it feels better is when I soak in a warm bath, which I have done a couple times. Could it be a cyst? Or maybe just an ingrown hair?