hi saltire!
I went through a period with the same sort of symptoms but with crippling migraines and bad headaches thrown in. I also got very painful lumps on my joints (that you could feel and see - very odd!).
Doctors were completely useless - told me the headaches couldn't have been migraines because migraine pills didn't work and then accused me of taking too many painkillers and then told me, I must be depressed! Illnesses that were considered - Lupus (and other related auto immune illnesses), fibromyalgia, arthritis, coeliac disease (you may want to get these ruled out).
Anyway, to cut a long story short, it seems that I have some sort of problem with my body's reaction to hormones. There's nothing wrong with my hormone level - the only anomalies in my blood are anaemia and a lower than normal white blood count - however, it seemed that my symptoms were quite often cyclical (based around my menstrual cycle). My menstrual cycle has been stopped and lo and behold, all my symptoms have either disappeared or lessened to the extent that they are hardly noticeable.
The gynae hasn't ruled out the possibility that I have an underlying condition that may have just been worsened by my cycle but at the moment, the thought is that most of my symptoms were being caused by a very severe form of PMT then getting a very heavy period was knocking my body for six and making all the health symptoms last longer.
I also can't emphasise enough how important diet is in all of this. I was advised to make sure I was eating a lot of carbohydrates and to have regular snacks to avoid my blood sugar from dipping too much as this also seemed to trigger problems. The IBS symptoms are a pain (and luckily, I don't suffer too badly in this department) but I have noticed there are certain foods that trigger those symptoms (spicy foods and beer for example) so I try not to have those too often.
I don't know what else to suggest but I'm so glad the doctors are listening to you. Mine didn't at all and I had to self refer myself to a consultant before I got listened to. Let us know what they say and how you get on.