Dear John,
First, a cystoscopy can rule out a tumor and help you move on, but it is not the only thing that a cystocopy can check for. The doctor can see if there's any inflammation in your bladder causing your symptoms. So go ahead with it and be done with it. The information we have is too limited for any of us to know if every test has been done. We don't know if the urologist has evaluated your stream, checked your bladder capacity, checked for post void residual.
What we do know, is that those of us here on the forum were ready to fight for our lives when we found out we had cancer, and yet you, at 19, are talking about giving up without even having such a diagnosis. I can't help wondering, whom do you turn to for support? I know you're not a kid, but are you talking to your parents, other family members, friends? It's great to turn to us for what support we can give, but it sounds to me like you need some more hands on support. Your stress, anxiety, and depression could be contributing big time to your symptoms.
Have you considered getting couseling? No matter what your final diagnosis is, it sounds like you could use some help in coping... with the future, and with the here and now.