If you have not used a condom during the intercourse, then it is possible that you have contracted an infection from the foreign flora of the rectum. Blood in the urine is a serious symptom and it should not be neglected.
What you need to do now is visit your doctor, for him to perform the necessary test and prescribe you the treatment.
When the infection will be determined your doctor will tell you if your partner also needs to be treated, most likely not.
I would not worry too much if it is just slight spotting. This can be just a water infection. I seem to suffer quite bad with urine infections and get them quite often, sometimes there is blood in my urine as just a part of the infection.
First thing i would do is contact your doctor, it may be nothing but worth getting checked out anyway. Be honest with them and they will be able to help!
Let me know how it goes