Prashant69 highlighted all the right points for you to consider. Feeling secure is one of the top reasons for your lack of pleasure. The fear of being infected, the fear of being seen approaching a prostitute and the fear of under performing (Premature ejaculation) might be causing you to not enjoy the sex.
When you say you visited 'many' prostitutes, do they all share the same attributes - height, personality, figure and so on? Because, you may not know this but I believe that some of us have very specific things we look for, that please us. Example - you may like women who are tall, well gifted on the front and who talk dirty. May be you are visiting someone who does not fit that profile and that could also be a reason for your unhappiness.
Over all, you are playing a dangerous game. Sex with any outsider, especially multiple outsiders is risky. I am not saying because you are visiting prostitutes, as many 'normal' people do have sexually transmitted diseases as well. Use protection to avoid the fear of infection. Make friends, may be you will meet someone who wants to be your friend with benefits. I am sure there are many such 'friends' out there, so expand your search area. Like Prashant69 said, once you meet someone you like, may be you wont need to visit anyone else and with the right chemistry, you can enjoy sex the way it should be.