About a week ago I started getting a mild ache

Patient: About a week ago I started getting a mild ache in my lower left abdomin, it’s not that bad more uncomfortable than anything, although when if first started it was stronger. It is worse in the evenings. Then when I had sex with my husband I got a deep stabbing pain in the same area. I went to see a GP and he dismissed it as ‘muscular’ but it won’t go away and I’m now nervous to try and have sex again, which is a big issue as we’ve just decided to start a family. I came off the pill about 4 weeks ago and, if it comes as normally, my period would be due next week. What could the problem be?

Doctor: