Dear Go-To Girl,
First of all I want to assure you that I am a consistent and correct user of condoms. Except, you know, when I'm on the rag. Then my boyfriend and I like it raw. Sounds good, right? Except, here's the rub: the last few times we've had period sex sans condoms, I get a mild painful feeling evocative of past urinary tract infections. I don't know what about having sex on my period could possibly be causing this; is my blood infected with nasty bacteria? Is God punishing me?
Congratulations on being a part of the .0000001% of the world who correctly and consistently uses condoms. Seriously, way to go. The only group more exclusive is the regular flossers, who count Go-To Girl among their ranks. What can I say? I love my teeth and gums. And I kinda like it when my gums bleed--like I'm whipping them into submission. But enough about me.
Sorry about your UTIs--few things are worse than a UTI in full effect, so I really sympathize. While it may seem that God is punishing you for having unprotected sex, there is a much simpler, less Old Testament-y explanation for your discomfort.
Contrary to popular belief, semen (aka, "cum") is not an inert substance; it is highly alkaline. (For those of you who didn't take 5th grade science, that means it has a very high pH) The alkalinity protects the wee sperm from the acidic vaginal environment so that they can make their way up into your egghouse and whatnot.
Under normal circumstances, the vagina has an acidic pH and has a mixture of yeast and bacteria that maintain it. When either your yeast or bacteria is out of balance, you know it: you have a yucky yeast infection or unbearable bacterial vaginosis, respectively. Both totally suck, and mean that God is in fact punishing you for having sex outside of heterosexual marriage. Just kidding!
Certain outside influences--hormonal contraceptives, douching, and semen among them--can alter the vagina's pH enough that bacteria or yeast can overgrow and cause nasty problems (each pH extreme allows the overgrowth of one or the other; you'll never have both too much bacteria and yeast at the same time).
In your case, your boyfriend's super-sperm is changing the pH in the vagina enough that bacteria are becoming dominant and, most likely, making their way up into your urinary tract as that cum oozes out of you. And, you guessed it, bacteria in the urinary tract is the cause of those sucky UTIs.
Here's a few ways to prevent this problem, in descending order of realisticity/desirability:
*Use condoms, even when you have your period
*Have the boy pull out and come on your face
*Pee right after sex
*Rinse your area thoroughly with water after sex and let all the cum drip out (seriously, all of it)
(I'd like to note that when Crotch Rot called her gynecologist, s/he confirmed my belief about the semen pH/UTI connection.)