I'm going to assume this was oral sex without a condom.
When did this happen?
So unprotected oral sex puts you at risk for syphilis, genital herpes type 1, gonorrhea and NGU.
Syphilis isn't that common, and she'd have had to have a sore in her 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.
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 you were with her.
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, 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.
Pain at the bottom of your penis sounds more like anxiety, but test if it will put your mind at ease. There is definitely a risk here, but oral sex is lower risk than intercourse.
Ok I’m now starting to feel a slight pain near the base of my penis
Please can anyone help? I just showered and my penis looks to be a bit discolored.