Unfortunately I can't give you much help, but I just wanted to say I had the same. I always get mittelschmertz - in my teens it was so bad that sometimes I couldn't move for hours, a number of times I thought it was an emergency only to find that it was something so benign! After I went on BC it eased up massively, but in pg I was advised to no longer use oestrogen-based BC due to family history complications, and progesterone-only was awful for me, so since giving birth to DS (just over a year ago) I have no longer been on BC. My first ovulation after the birth, I was curled up on the bed, on my knees, biting the pillow and yelling 
I just had to ride it out 
It eased up a bit, then started to get worse again. I went back to the GP, they ran some dietary tests to make sure it wasn't that, then sent me for some hormone tests (day 2-4 and day 21, feeling around my abdomen for swelling etc). Slowly I started to get better anyway, and the tests came back as being fine. I only get regular pain now - twinges, or a dull ache, not awful pain.
I never bf'd and periods returned quite quickly, when DS was about 6wo, so it has taken a little while to settle but it has settled. I have found naproxen to be more effective for this pain in the past, so if you haven't used it before it's worth a shot, I've also used cocodamol. I've no idea if you can use naproxen whilst bfing, but you can use cocodamol/codydramol (one, or both, of these, I don't really know the difference! But I was prescribed it postpartum on the basis that it was fine to bf whilst taking it).