Transmission?

I drive a 2003 Saturn VUE and just recently hit 100,000 miles. About a month ago, it started acting up. Everytime I stopped at a red light or stop sign and then accelerated on the gas pedal (not aggressively, normally) the RPMs would rev up and the car would go nowhere. It was as if the car was put into park and I was revving up the engine. It would do that whenever I tried to go and if I let off the gas and slowly tried again it would eventually go. NOW it has gotten a lot worse and its whenever I accelerate in general whether it be at a stop and go or just increasing speed. Sometimes I have to let off the gas 2-3 times for it to finally go. It has put me in some dangerous situations with heavy traffic. What is wrong with my car? Is it the transmission? Do I need to have some kind of fluid changed? I don't really have much money so I'm hoping this is not a big issue and is something small that can be fixed.