If anything I had unprotected oral but that was about 2 and a half years ago since then and I had no issues, so the time window on STI's wouldnt match up either
I may also add, that I dont feel any burning or pain during urination, there would the odd occurence of a slight minor tingling sting after urinating but that only happens once in a while, sorry for adding so much responses I am just stressed out of my mind
Chances that this is an STD are low, given your sexual activity.
So let's look at the rest - it happens more when you wear tight boxers - are they too small, or just form fitting, like boxer briefs? If they are too small, it would be worth the investment to buy some that actually fit.
Another thing to consider is if you are dehydrated. Even being a little dehydrated can cause irritation in your urethra. How is your water intake? How much caffeine do you drink? Caffeine is really irritating to your bladder and urethra, as is alcohol, and neither do anything good for anxiety.
Could it be a hyper-awareness of the area because you are anxious about STDs? I don't know which came first for you - the anxiety about STDs or the symptoms, which then caused the anxiety.
How is your hygiene? Especially if you have a foreskin, are you cleaning the area regularly? Do you use a gentle soap? You don't need a strong, scented, "manly" soap.
By all means, get it checked out and make sure you don't have a urinary tract infection or anything, and get tested for STDs if it will put your mind at ease, but also consider the rest.