Three different garages including the dealership cannot find why my starter is not working?

My car did not start. Took it to a garage and they said it was the battery. Replaced the battery and it was good for a few days. Car doesn’t star again intermittently. Diagnosed as the ignition switch. Had that replaced. Car worked for a few days and then had intermittent starting problems again. There are times my car has a “jingling sound” coming from underneath the car. Then I was driving and the RPM's were jumping up to 3 but my car felt like it was going slower and that it was going to stall. They said my throttle body was dirty and they cleaned my whole fuel system. Same day my car starts having trouble starting again. I made an appointment with the dealer. They said it was the ignition switch (again) and my serpentine belt was stretched and both were replaced. I picked it up last night and today I have trouble starting it again.
three different garages including the dealer lots of things checked and no real answers. Please help!