Age could be a factor.  Also if you are on medication. Some medications could have an effect on your "cum time" too.

If you run to the appointment then take a quick shower, studies show that brisk walking, running, weight lifting, physical exertion right before intercourse advances significantly you threshold to orgasim.  Try it.

I swim 2-3 days a week, and also lift 3 days a week. Cut out the smoking. Smoking impacts the ability of the erectile tissue to repair itself at night. Lets not for get about getting your 8 hours of rest. Diet is key and the time of the day. I usually like to have fun about 1 hour after I eat, make sure you eat protein with each meal. The bigger ladies will require more energy and time to bust the nut than the smaller ones usually. Some times he smaller ladies have a big pussy that require a lot of strokes before getting the pops out.

You can also do some extended foreplay before the penetration starts. Make sure she sucks your dick to it is rock hard before penetration starts. Do more kissing. If she is a submissive put some restraints on her, that can increase excitement for a big pop.

you smoke and drink, run on the tread mill 30-45 mins a day, fuck for 2 hours, prolly jack off for another 30 mins to cum... SOUNDS LIKE YOU'RE TIRED lol.

all kidding aside, it sounds like you need to relax. i find it easier to pop a boner and cum hard when i m rested and relaxed. before i see a provider i usually don't jerk off for 3 or 4 days and do something i like, perhaps riding motorcycles, enjoy the weather, go to the bar have some drinks with friends or whatever. then when time comes, i look forward to my appointment. don't rush it, just relax. maybe its the providers you're seeing too?

Sometimes I can cum right away, but I try not to. Then i get used to the feeling and can't cum.  Condoms reduce the feeling to me.  I am lucky if I can cum 50% or two-thirds of the time.  Try the health thing that people mentioned, but I think relaxing is important.  Even though it's nice I wouldn't worry as much if you can't. When you worry too much it becomes a hinderance.  Only once in a rare while will I even attempt a second pop and it's super rare.