[Do you know if you can have TOS but have normal test results (mri, emg etc.)?]

Yes, it's one reason many drs don't know a lot about TOS - it doesn't have any specific test that will prove it easily and undeniably.

And a very good reason to seek out the best expert PT /DC / bodyworkers that you can find.

What kind of swimming laps with the same stroke style (very repetitive) or varied recreational swimming - lots of breaks and floating?