I have a very tight foreskin and the head of my penis is very sensitive

I am 21, and am uncircumcised. I have always had a problem where I cannot retract my penis past my head, and I cannot even touch the head of my penis as it's so sensitive. I have tried stretching exercises, even with cream prescribed by a GP and I still can't retract it as it will hurt. I haven't had sex as I know it will hurt a lot even with a condom. I have no problems masturbating. I am unsure what to do, I've booked a session with a GP in a couple of weeks but would like some advice in the meantime. Has anyone had this problem and if so have you been able to have sex without it hurting. It seems my frenulum is attached and is very short, but that isn't what's stopping it from retracting

What you may have is Frenulum Breve - you may be better off going to a Urologist rather than back to a GP about this. The sensitivity with your head of penis will most likely be linked to the fact that it has had minimal exposure - in terms of sex, if you can masturbate ok then the act of penetration should be no problem for you.
The Urologist would likely recommend Frenuloplasty which is a minor procedure, you should not entertain ANY suggestions of circumcision until you have tried this first.
When you were trying to do the stretches over what period of time were you doing these CONSISTENTLY? Also, were you doing the stretches during, or immediately after a warm or hot shower - as this greatly helps the process?

what happen if i pull my dick hard in order to break that frenulum?

The frenulum is a natural part of the penis, you should not even attempt to damage or break it.
Why are you thinking of doing this … ?