What Causes A Lump On Vaginal Lips Post Hysterectomy?

Hi I had a vaginal hysterectomy 30/01/2015 everything went amazing and I m back at work now but 2 days ago I noticed a lump on my vagina lip thought it was just a cyst as I usually get them but this one is large and bruised very hard and hurts to sit and walk. I haven t been wearing usual underwear just big knickers since the op and have intercourse once last week after the all clear I m worried as it hurts so much I ve tried to squeeze it like the other cysts but it won t burst please help