I played alongside a gentleman that had given up the trumpet for about 45 years. He told me the best advice ever given to him (by Chuck Findley) was to forget he ever knew how to play the trumpet. It's not like riding a bike. Your brain might remember how to play but your muscle memory is gone. So, with that, think about being your own teacher as opposed to just picking up where you left off. You know what you're doing - it's just a long process to train your muscles to cooperate again. Trumpet playing, for lack of a better term, is a real bitch sometimes. I've never stopped playing and I struggle to improve, too. My humble advice is to do exactly what you're doing: stay patient and keep at it; and when you lose your cool, ask for advice. I joined forums for my trumpet, my guitar, and my car. I find it to be a great way to get perspective and to keep from feeling helpless when I run into a problem.