I have experienced similar problems from time to time, and I think this is a part of the problem.

Through out most of my life, I think that a lot of the times that I would piss, I would be putting pressure behind my stream to help push it out quicker or something?

Well, I think if you have done something similar, you've built a tolerance to patience, and muscle relaxation..

So, maybe our bladder is used to working out while it is pissing? It's not used to just flowing freely and effortlessly..

So, from now on try to almost meditate while pissing on using no muscles, and keeping a comfortable pissing process. Because I can imagine being frustrated not getting any urine out as fast as you would want to, so you kind of try to push it out, but try to just be as normal and natural and relaxed as possible.