It was a long and painful process unfortunately - I'd always had bad period pain right from the first one at 13, was first given mefenamic acid at 15, and plodded on through my 20's being told I had IBS, my pain was normal, some women just have bad periods, etc etc.
Mid 2014 I became chronically constipated and started passing a lot of mucus from my back passage. When to the GP, who did a few blood tests for colitis and coeliacs etc. These all came back normal and he said it was IBS. I went back again March 2015 because I was having increasing problems with my periods, which were lasting 10-14 days and often so heavy I was having accidents. He said it was because I was perimenopausal (at 37). I asked if it could be endo, he told me I didn't have the symptoms. In May 2015 I collapsed at my son's swimming lesson with abdominal pain. I was terribly stressed and frightened by that point but didn't go back to the GP as I'd been told it was all IBS and my age. It happened again during my period in June, and then again in July. That time it was so bad my husband called an ambulance and I was taken to A&E with suspected appendicitis. They ruled that out and said they thought it was gynaecological and I should go back to my GP and ask for an ultrasound, which I did. He also then did the ca125 ovarian cancer blood test. That came back abnormal at 119, which put the GP into a complete panic and he told my husband and I over the phone on a Friday afternoon that I probably had cancer. We waited 5 horrendous days for an ultrasound. That ruled out cancer but they did find what they called paraovarian cysts, and a hydrosalpinx in my right fallopian tube. They told me it didn't warrant a referral to gynae and told me to go back to the GP.
It was about 6 weeks before I could get back there, and I went to see the practice nurse. I talked through everything with her, and she referred me to gastro for a colonoscopy, because she said my bowel symptoms should have been investigated properly back in 2014 and had not been. She also sent me to see a different GP at the surgery, who specialised in female health. She said straight away that it was endo. I had the ca125 repeated twice more (it went down to 85, then back up to 107) and was referred on to gynae. The consultant said he was sure I had it, and this was confirmed by lap in January 2016. Once I found a GP who would listen it was straightforward, but getting to that point was far more difficult than it should have been.