I asked a similar question not too long ago. Here is my medical profile. I don’t have STD, I am not taking any pills, I am in my mid 20’s
I do however have irregular periods which I may get them every 2-3 months at a time.
I am in my mid 20’s, no kids, not pregnant.
Just 2 days ago I started having sex with my new BF. I have been sexually active for 2 years now and has never experienced any bleeding from my past boyfriends. My new BF is more well endowed and we did engaged in very rough sex which we just started 2 days ago and only 2 days ago. Also we did used condoms for protection. And yes there was use of lubrication

There was no pain after we had sex except for the morning session in which I was dry and asked him to stop before we could completely go through with it. 5 hours after we parted I noticed some slight bleeding as i cleaned up myself. later on that night my panty liner was stained and I switched to wearing a pad.
I browsed through the internet about bleeding after sex. They say rough sex can cause this but should not last more than a day.

There is no pain, but do do feel a bit bloated and some light abdominal pressure similar when you get a period. I feel no burning or itching sensation at my vagina as well, but I feel similar to having a period.
The blood is not pink but red, or deep red, with small clots from time to time. I dont feel dizzy either or nauseous. And yes there is a lot of blood similar to like having your first or 2nd day of having a period.

I contacted a doctor who told me to monitor myself for the next 6 days. If the vaginal bleeding was cause by rough sex, he informed me that I just might have a tear and needs to not have sex for a while till it heals. I am still bleeding as of now.

My friend also said that the sexual stimulation may cause to trigger a menstruation.
I would like to know if this is possible for some one like me who have an irregular period?

Or if this is caused by rough sex how long does this take before it stops?