Just relax man!
You are still at a point in your life where you have options. Considering you are running what appears to be quite a successful business and going to school fulltime and managing to have as much of a "life" as you can outside of your work/education, stress is something that comes with the territory (I'm sure you know that already though). Your choice to continue your education and actually get a degree (and one that actually means something) is awesome.
The best advise I can give you is to do something that doesn't involve work or school. I know it may be tough to find time in your busy schedule but find a "hobby" or something that you enjoy doing outside of work and do that every week. Whether it be something like karate, softball, collecting something, etc., you just need to find something to take your mind off things.
For me, my Fire/EMS career is somewhat of my "get away". While it can be stressful doing the training and continuing education, it all is worth it. When we have that medical emergency call at 11pm for an elderly person in cardiac arrest, that is my get away. When I am running that call, everything else in life seems to just go away...I don't have to think about that test I have in class in 2 days, I don't have to worry about the 5 page paper I have to write for my ethics class, I just have to think about the scenario right in front of me. Even though I am paid to do this stuff, I use it as my get away a lot and it takes my mind off other things in life.
I really think you will benefit greatly if you can find something to take your mind off things. Just do it a little bit every week to help keep your stress levels down.