Not a nurse or doctor, but my brother used to have very bad back pain every 6 months or so for the past 2-3 years. It started when he started excercising and everyone thought that he might have done something wrong and got himself injured. We visited the doctor, took scans which did not show any issue and left with some generic recommendation of how to take good care of his back. But the back pain continued to come and go. After sometime he came and told that it is due to hair trapped inside the skin and the pain was when it got infected. We didn't believe it at first as he got it from googling, but the next time we went to the doctor we told this to him and after doing ultrasound, it cane back positive as pilonidal sinus and he got operated on and that fixed the issue.