Breast implant illness

Hi what are the symptoms for breast implant illness and capsular C? I’ve got 375cc high profile round smooth Johnson+johnson silicone implants under muscle through MYA and I’m really worried somethings wrong with my left breast, feels different to touch, occasionally get pain in it and I’m constantly tired with brain fog and have been ill loads, also get occasional shooting pains in top of my back which I’ve only had in the last 3 years since getting implants? Please tell me some of the signs to look out for and if I should get checked over, if something does happen do I go to NHS gp or will I have to go back to MYA? Side note I had horrible “less than an A cup” tubular breast and was so depressed over them so would be gutted to have them removed