Dovod, some of this is not about the trumpet. When you see a key signature, figure out what the key is. Remember that it could be a major key or a minor key a 3rd lower. Once you have that established, play the scale for that key (this on your own, BEFORE rehearsal). Work that scale every practice session. Find it in Clarke (it's there - if a minor modify the corresponding major). Play the first 3 (at least) exercises in that scale.
You know in your head what the scale sounds like, so you don't even need the music to practice once the key is established. The only reason to count flats or sharps is to know the key - how many there are doesn't matter and just gives you a mind *&^k. The mental part will do you in if you let it.
Play a C# scale and note the fingering. It is actually easier to finger than C. We learn that it is harder early on in our training, because of all the #s. But it is not.
Do yourself a favor and get a copy of Chase Sanborn's Brass Tactics: ยป Online Catalog
I believe it will help you make a breakthrough. (Not affiliated with Chase - but he helped me!)