What Causes Vaginal Tenderness, Pain And Bleeding After Intercourse?

My boyfriend and I have been having sex for about 2 months now...and because of our schedules it may only be once a week to once every other week. I have noticed that my vaginal area is tender and slightly painful till about a day or 2 after. I also noticed that there is a little blood (paper cut amount) that is the color or watered down blood. He is well endowed and so I have been attributing whats happening to his size and the fact that maybe I have not gotten used to his size because of not having sex more frequently. Could it just be that i am not used to it yet becuase there is a larger gap between times which we have sex? Or do I need to be more concerned about it?