Yarnball..... I might be able to help.....it would help tho, to know what year, make and model your machine is........... .this was happening to me a few months back with my machine and I got so frustrated I put it on the shelf til I could afford to take it in for repairs.
Well, hubby and I bought a book on sewing machine repair instead...spent about the same amount of money as it would have cost for an hours work at the shop.
Found this out by reading the book and did this to my machine and it works fine now.
There is a plate UNDER the machine with two screws.....I took those screws out and removed the plate and found THIS!!! (see photo) Cleaned that out, put some grease on the gear that is under there (just a drop) and put the plate back on and VOILA!!!! The machine worked FINE after that!!!
SO....before you spend $50 or more at your machine shop, try that!!! CLEAN and oil it!