What Causes Vaginal Bleeding Every Time While Having Intercourse?

I nearly always bleed during intercourse, regardless of the position and gentleness of the intimacy. I ve been tested for STIs (neg), had ultrasounds which only show some cervical cysts, an endometrial biopsy showed nothing and previously I was treated for cervical ectropion (sp?) and there s no indication that new treatment is needed. The bleeding is heavy (think massacre) and bright red and can last a few days. Sex doesn t always hurt. The gyne says my boyfriend must be too big for me. This has happened to me with one other partner. It s never been an issue for him before and frankly, he s only slightly larger than average. Is it worth a second opinion or is this really possible? I ve had two vaginal births, kids are 7 and 9.