What Causes Bleeding After Non Penetrative Sex?

Recently i've became somewhat intimate with my boyfriend, however we haven't had sex. He has fingered me, and recently i've been bleeding everytime about an hour after it happens. Before we have done this and it never have turned out this way. I've just recently started taking the pill as well, so that might be the reason. He also does it pretty intensly which doens't hurt me at the time, but i've also read that could be a reason as well. What do you believe this is? And is it serious?