I am sorry you are feeling so unwell; please understand that online no one can state what anything is with any certainty, all I can do is offer my best guess based on what you've written.
There may be several things happening here at once. Constipation like what you describe can tear the anus and cause bleeding (anal fissures). That is potentially one source of the blood. Straining at stool may also cause hemmorids, which can burst and cause blood as well. Activated charcoal is a cause of constipation...it is mainly used in poisoning cases and there is not good evidence that is effective in bloating or reducing gas. It may be causing some of the discomfort that you feel as it can cause constipation. I would stop it were I you.
I think maybe you pulled a muscle in your back; that started yesterday after a work out but I cant totally dismiss the possibility that its related to the other symptoms and you did not feel pain there until now because what you have is worse. But I do not believe so.
Your stomach discomfort is a more difficult one. Low level pain like that can be from many causes; its severe and agonizing pain though that is most commonly from life threatening ones, so as uncomfortable as you may be, I do not so far think you are in acute danger...at least from what you've written. I am wondering if it might be some sort of ulcer, as they can be more uncomfortable after you eat, depending upon where that ulcer lies.
Though I think you are not in acute danger I DO think you need to see a doctor because discomfort like you have for two weeks is not something that should be ignored. Neither is the anal bleeding that you have. I can not say online where it stems from and only an in person exam can do that. You may have an anal fissure that needs some repair.
As to the STD issue...not specifically, no, but your cloudy urine does make me think you should be checked for a UTI (urinary tract infection). Its possible during sex she passed the bacteria to you and so you acquired it that way. A prostatitis (infection of the prostate) also potentially could cause some abdominal discomfort. For that you would need a doctors exam and antibiotics to treat it with.
Hallmarks of STDS are generally a vaginal or penile discharge, or a rash. Although some can be asymptomatic, meaning that the person does not even know they have it.
I read that you don't have medical insurance. There are many free clinics and low cost clinics. Here are some web pages to help find them; I do think a doctors visit is a good idea given what you've written. And if the pain were to become agony, an Emergency Room visit is a good choice. http://www.needymeds.org/free_clinics.taf
Here is a link to common STDs and their symptoms: http://www.fwhc.org/health/std.htm
I hope I was able to help, and that you feel better soon.
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