Go to the doctor, get checked out and ask about the IUD. But if everything is normal you might just be too tight. If thats the case you should wait a while longer to have intercourse and maybe look into buying a set of dildos designed for stretching the vagina, they usually come with six of different sizes. You start off with the smallest and graduate to the larger ones. You don't want to rely on using fingers to stretch your vagina, fingernails and the shape of a hand can make that pretty uncomfortable. You and your boyfriend can use the dildos together till you're ready for another try.
Hello,
It can be due to bleeding due to trauma during intercourse. The vagina and vulva are delicate, yet resilient structure made of skin, mucous membranes, muscle and so forth. The lining of the vagina is very similar to the tissue that lines the inside of your mouth. It's soft, squooshy, and it bleeds when it's cut or roughly rubbed.
Avoid masturbation and intercourse for some days and if the symptoms persist then get it evaluated from a gynecologist to get post coital bleeding ruled out.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
It will stop soon. The first handful of times will have blood, though.