The reason that you get shoulder pain following a laparoscopy is because the carbon dioxide they pump into you irritates the diaphragm which shares the same nerve supply as your shoulders. I suppose you could maybe have endo on your diaphragm which causes the same effect during your period. I just searched 'endo on the diaphragm' in the search box and there are lots of other women experiencing the same thing. Have a look.
The first hurdle in getting a diagnosis is getting past your GP. But even if you get your gyne referral they may not be endo specialists. I saw a gyne who said my endo on my bladder and uterus could not be treated as this would risk damage to these organs however I’ve been told on this forum that endo specialists can operate successfully on this. If you can afford it see if you can get a private consultation with a gyne who specialises in this area, it can cost around £200 but may get you somewhere and they can refer you back on to the NHS for treatment.
Regarding food have a look at the endo diet. endo-resolved.com/diet.html
Hormone treatments are the best thing to help with endo e.g. pill, coil etc. as no ovulation = no period = no pain but no good if you want to start a family. I’m not the best person to ask about hormones as I’m TTC but other ladies on this forum can help.
Hope you get some answers soon xx