HIV is not a risk here. Let's get that out of the way first. Even if you had a sore on your anus, and she had blood in her mouth, or whatever, that's not enough blood to transmit it, and saliva has an enzyme that breaks down HIV. The rimming and oral sex are not risks for HIV.
However, there are some risks to receiving oral sex and rimming.
So receiving unprotected oral sex puts you at risk for syphilis, genital herpes type 1, gonorrhea and NGU.
Syphilis isn't that common, and your partner would have had to have a sore in their mouth to transmit it. You wouldn't see symptoms of this for 10-90 days, but the average is 21 days, and you'd get a sore called a chancre. This doesn't cause burning, pain, discharge, etc. You can test for this at 6 weeks. If you get symptoms, but test negative at 6 weeks, test again at 90 days, and get to the doctor as soon as you see symptoms.
If you don't already have herpes type 1 (think oral sores, like cold sores but not canker sores), then you could get genital herpes type 1 from receiving oral sex. This can happen even if the person performing oral doesn't have a sore, but it's more likely if they do. The time from infection to symptoms is usually 2-12 days, but the average is 4 days. You can test for this now, and then again at 4 months to make sure you don't have it. If you test positive now, it's a pre-existing infection that you had before this encounter. About half the adult population has this, and 90% don’t know it. Ask for a type specific IgG blood test.
You'd see symptoms of gonorrhea at about 2-5 days, and this would usually be a discharge, burning, etc. Some people don't get symptoms. You can test for this as early as 3 days, but 5 days is better. You can have a urine test or a swab test.
NGU is an infection in the urethra that is caused by anything other than gonorrhea (nongonococcal urethritis urethritis, sometimes called NSU, for non-specific). This can be caused by normal mouth bacteria entering the urethra, and the symptoms and testing times are the same as gonorrhea.
Rimming is all the same, with the exception of NGU, which doesn't apply to the anus.
The dull, throbbing pain could be anxiety, or it could be the start of an infection, like gonorrhea or NGU. If you've had it since shortly after your encounter - as in within hours or a day - it's probably anxiety. If it started after 2 days, it is more likely to be an infection.
It could also be dehydration, irritation from caffeine or alcohol, or a host of other irritants. You really should get it checked out to be sure.