Usually SSRI's decrease premature ejaculation. In fact it can make it downright difficult for some to ejaculate at all.
Most 20 year old males get exited quite easily, so don't worry about that. it will most likley decrease with age.
As one who suffers from General Anxiety Disorder and severe panic attacks (and depression) from my experiences, you have to learn to try not to worry about everything under sun. Get checked by a Doctor if you need to, but most likely everything is just fine.
I can help with your bladder shyness. Yes, an anxiety disorder can aggrivate being bladder shy. However, it is not the cause of being bladder shy. I am bipolar and one of my symptoms is anxiety and it aggrivates my bladder shyness. When my anxiety is under control I have an easier time using the restroom in public, but I still have to psyche myself out. It is something I have suffered since I was a little girl and I am now 33. Being in college helped me a some, due to the fact that I had to go with other students in the bathrooms. I had no choice. I do have this re-occuring nightmare that I am sitting on the toilet and there are people surrounding me and I can not pee. I always wake up and have to go. Whenever I have this dream, it causes my bladder shy symptoms to triple and I can not use a public restroom for a long while, until that phobia calms down again. Several years ago I did research on bladder shyness. It has a long technical name, I forget, but it is referred to as bladder shyness. This "phobia" is a psychological anxiety where the individual can not urinate unless in complete private. It usually stems from a childhood event involving the child using the bathroom. Usually the child is tramutized during potty training and bladder shyness is the result. When I read that I remembered that my mother let my aunt (her sister) potty train me. She was emotionally and verbally abusive with me during my potty training. She would come into the bathroom and stare at me on the toilet until I went. It gives me shivers just thinking of that hateful stare. Anyways, I usually could not go, because she did not give me any privacy or gently encourage me to go. She always stared and then yelled at me saying she was taking away privledges. BTW, she trained me because I refused to cooperate with my mother, so my mom let my aunt have a go at it. When I was too scared to go, I would get up and rush off. I would always mess myself and then she would yank off my underwear and wash them in the toilet in front of me. When I gained insite to why I am bladder shy, what she did made perfect sense. Thankfully, years ago, my mom ended her relationship with her sister due to a bunch of family ****. I hope this story gives you insite in figuring out why you have this condition too. Once I got that knowledge, my nightmares did ease up and I do not have them very often anymore. I also can use a public restroom alot better, it takes me a few minutes, but I can do it. I also created a "Pavlovian response" for myself. I taught my brain that when I blow my nose I react by being able to pee. Hope his helps you some. Take care.