I lost my tennis strokes as a 15-year old, how can this happen? And has someone experienced the same? (maybe with another sport)?

So in the summer of 2017 I was playing in the highest tennis category in my country, but then I suddently lost my service, what wasn t that bad because I could still hit my other strorkes good. But then in the winter of 2017 I also suddently lost my forehand (my backhand is still good), my trainers said I was just overthinking things and that it will come back with practise but it didn t. I have gone to a psychologist, but that didn t help (not with tennis problems at least). I have now not played tennis for 3 moths and have had some kind of threatment (psychomotoric) from a physiotherapist, but I don t really believe that that is going to help either. I m now getting a scan of my shoulder and neck, because my doctor thinks i have some kind of nerve/muscle problem. I didn t really have pain when I lost the strokes, but my shoulder has been getting stiffer even though i wasn t playing as much and now i sometimes get a kind of cramp feeling in my shoulder it s a bit diffuclt to describe. So if you have experienced the same or know what this is please help. Thank you!