Pain down below

Eva • I`m 27 years old and I`m married. I'm the proud mama of a 1 year old beautiful baby girl and step mama to a 7 year old beautiful little girl. Baby girl #2 is on the way!
Does anyone know what an on again off again pain in the vagina wall on the left side could possibly be? When it comes, it hurts pretty bad. It lasts for about 10 mins then gone.