I'm glad you posted and will try to provide you with all the information you need. Could you tell me what in this has you thinking about HIV?
HIV does not manifest as burning upon urination or pain in your lower back. When one gets HIV, initially it can be flu like symptoms. Then, typically, (if one was infected) years can go by before people start having symptoms from a depleted immune system. None of what you've related here makes me think HIV has anything to do with your symptoms.
If your partner tested negative at that time, it means she was not infected 3 months before she took that test. So, if you test negative tomorrow, it means you didn't get it 3 months ago or anytime before that. It'll also mean you can relax about HIV.
Sometimes when there is pain in the genitals, we want to jump on the STD bandwagon. Although that's a good thought, it's not always the cause. Sometimes just the fact that there was a lot of sex and friction can be the cause.
Let me know how your test went and if you have other questions, okay?