Greetings.
No, you symptoms are not suggestive of STI. I am not even sure why you think STI, since none of the symptoms you described is STI-specific.
I suppose you suspect STI because you have unprotected sex with multiple partners. In this case regular STI testing is a good idea, with or without symptoms.
No, it is definitely not gonorrhea. Gonorrhea is a kind of acute urethritis with very distinctive pain and discharge.
Testicle pain and discomfort is an alarming symptom. If the pain is regular and recurrent it might be a surgical problem. You may need to see your doctor about it and get a referral to a urological or general surgeon.
It is not possible to answer "What else could be" over the Internet. It could be lots of things, but most probably it is just your worries. Anxious mind fixated on symptom can feel a lot of strange things.
thanks, I'll be sending off my sti sample soon anyway just to be sure but there is also the incubation period so it's tricky to know when to send it. bit alarmed when you mentioned a surgeon. i'll be seeing my gp about it again soon or the sexual health clinic