Welcome to tennis. Being new to the game, you can be a great athlete and easily lose to out of shape non athletes that have played for a while. It is a tough sport in that someone that is just slightly better than you can often beat you very easily. It is great to play people better than you. If it is too lopsided it is no fun for either of you.
You will enjoy the game more if you find a league with people at your own level (there is a reason that USTA doesn't have 3.5's playing 5.0's). If you play 3.5 and win almost all of your matches you will get moved up to 4.0. Eventually you will find a level that gives you a good mix of players that are better and worse than you. As you improve you will move up.
Yes, you are just playing with people that are too far above your level now. If you subject yourself to a beat down every time you go on the court you won't last long in the sport.