Forgive the pun...but sorry for the long winded reply!!! There is no quick and easy answer but in time you will find your way. The surgery you had makes the bowel very grumpy and it's not good to leave them unsupported.
Doctors know plenty about drugs, surgery, putting us back together after accidents, doing life saving transplants etc. (Some of them aren't even good at these things). However, they will rarely if ever send you home after surgery with advice on how to take care of yourself to assist a speedy recovery and longterm healing. This is largely because they haven't a clue and they feel they've done their bit. They also get nervous about liability. So it's important to recognise that there is a whole raft of things we can do to aid our own sustained recovery and heal from a major intervention into our body that should not be underestimated. It's important to know when to use modern medicine and to understand its limitations. Only then can we start to be more responsible for our own health and recovery.
Your bowel symptoms tell me that you possibly have leaky gut/intestinal impermeability. You might also have an infection or bacterial overgrowth in the bowel. Progesterone pills can cause diarrhoea so that's another thing to think about re the Norethisterone. Gluten intolerance (coeliac) or sensitivity is a consideration too. Cutting out gluten and dairy are often a first port of call in dealing with leaky gut as both are very inflammatory. This does not necessarily mean that they have caused your bowel issues or that you can't have these foods in future once your gut is repaired.
It seems potty to me that you are on a combined pill, Microgynon, with oestrogen in it which is the hormone that drives endometriosis. That's some hormonal cocktail you're putting into your body and the bowel is also affected by hormones. Hormonal pills also cause deficiencies...reading online the following are mentioned....magnesium, riboflavin, pyridoxine, folate, vitamin B12, ascorbic acid, zinc possibly others. They apparently increase the levels of vitamin C, iron, copper and vitamin A. Being aware of this means you can take steps to compensate and learn what foods and/or supplements to take. Personally I don't take supplements without advice from a naturopath. In time, you should be able to get your nutrients from your food once deficiencies are corrected through supplementation and your issues are resolved.
The fact that your symptoms occur after eating is interesting. The frequent diarrhoea will also mean that your digestive system does not have a chance to absorb essential nutrients from your food and everything is getting flushed out. Over time this will have a knock on effect and leave you tired, anxious, lacking in energy, brain fogged, depressed and open to further illness as you become progressively more deficient. You have already mentioned that you are tired all the time and are completely zonked. No wonder you need to sleep so much. Don't ignore these symptoms. Remember, you are only 3 months clear of major surgery which is very draining for the body.
Look up 'leaky gut' online and learn all you can. Plenty of good articles and advice but I feel that if you're overwhelmed with it that you find a good naturopath to help you. Here's just one overview article of many mindbodygreen.com/0-10908/9...
GPs and the NHS testing have their shortcomings but you could get yourself checked out for an infection at your GP. I don't know how good the nhs is on stool sample testing but it might be a useful first port of call. If an infection is found, be wary of antibiotics and think carefully before taking them. If you do take them make sure you get help from a naturopath on taking probiotics as well. While you're at the GP get a blood sample and get tested for essential nutrients such as ferritin, folate, B12, vitamin D etc. Any good GP will do this and if they don't, start demanding.
I am more familiar with dealing with constipation and can't recommend anything for your particular situation. I do recommend a review of your hormone pills (with a different doctor, possibly the one we discussed via PM). Also a trip or two to your GP to use them for more diagnostics. Then I recommend you follow up with consulting a good naturopath and show test results to them. I'll PM you one who really helped me.
I also recommend supportive activities like acupuncture, aromatherapy massages, hot baths with essential oils, daily walking (as much as you feel able - even 5 mins is better than nothing), getting good sleep, meditation, doing something creative etc. Getting better is a big project. Above all, be kind to yourself.