Welcome to the forum. Thanks for your question.
Bottom line: Little or no risk, no reason to worry, and you can expect a negative HIV test which will indeed be conclusive.
First, the odds a woman like your partner has HIV is nearly zero. Among heterosexual women in the US, HIV is almost entirely limited to commercial sex workers and the regular partners (usually wives) of HIV infected men -- not to sexually active single women. Second, if she had HIV the average transmission risk would be once per 2,000 unprotected vaginal sex exposures -- which is equivalent to having sex with infected women once daily for 5 years before infection might be likely. Third, your symptoms are not typical for a new HIV infection; both the nature of the symptoms and their timing is wrong.
Those comments pretty well answer your specific questions, but to be explicit:
1) Extremely low risk, zero for all practical purposes.
2) Presumably your urine test was for gonorrhea and chlamydia. The negative results are reliable and conclusive; you have neither of those STDs.
3) The HIV combo test is always "defiitive and conclusive" at 28 days. Here is a thread that discusses the time to reliable HIV test results, including the reasons most official advice remains 3 months even though reliable results rarely if ever take that long. As you will see, it in turn contains links to other relevant threads:
http://www.medhelp.org/posts/show/1704700
So all is well. In the future, I hope you will use condoms for non-monogamous sexual encounters -- why go through the anxiety you are now facing? But still the risk is low enough that you really don't need testing at all, and you can expect your reassurance test -- the combo test at 4 weeks -- to be negative. At that point you can forget this event and move on without worry.
Best wishes-- HHH, MD