Your bleeding might just be the result of vaginal tears, it can happen when you're not properly lubricated or when thrusting is too forceful. Kegel balls will help strengthen your internal vaginal muscles, but I don't think they'll help you prevent vaginal tears. Try a different position, e.g. woman on top, so you can be in control of how he enters and thrusts to avoid traumatic tears; and most important of all, use plenty of water-based lubricant during sex. If you still encounter bleeding after that, it's time to seek help from your doctor as your vaginal tear might be more severe.