Your Right, I like that...
There are many reasons for women bleeding after sex. If you research on this site you will see many posting similar questions as you have. Some women are on contraception, some only experience blood after they orgasm, some use condoms, some have HPV and some don't.
The most common reasons are the vagina tightening during sex (climaxing) and then once relaxing, releasing pent up blood. Others are tears from sexual activity, harmless infections which are easily treated but a lot of women find after tests that Dr's are stumped and have no clue as to why they are experiencing this. A lot of women go on to live with it, trying to change things like there birth control, how they have sex etc to change the problem.
Just to add in rare cases it can be a symptom of a certain kind of cancer. I feel I should add this just to give you as much information as I know but please don't jump straight into the worst scenario as this one is unlikely. Most who experience blood after sex do not have cancer. The kind of cancer is also found a lot more in older women