Cannot tolerate much fat or protein

[Zen123]

Ever since taking acutane in my late teens and early 20s (I'm 41 now), I have a hard time maintaining and gaining weight. Around that same time, I also got sick from cryptosperidium in the water in Milwaukee, and lost weight. I'm 5'11" and 142 lbs. and I'm often told I look too thin. I also suspect that since I was a premie/twin, I may have been born with a weak system, as I've always been very sensitive to foods.

The main problem is that I cannot eat more than 10g of fat ("good" or "bad" fats) a day (and not more than one meal a day) or about 20g of protein more than every other meal. I also can't tolerate most supplements. If I do, I get extremely tired, depressed, have trouble falling asleep at night, and then wake up exhausted the next day. It also feels like something in my lower right abdomen area is pulsing/pounding. It's worse when I eat oils and much worse when I eat fried foods.

I eat a very healthy diet: no dairy, wheat, sugar, coffee, and I don't smoke and don't drink much. I drink plenty of water. I've done juice fasts, herbal fasts, parasite cleanses, liver cleanses (couldn't tolerate the herbal liver cleanse, but can do the grapefruit juice and olive oil cleanse), tried raw food (lost even more weight), probiotics, and more. I exercise 4 days a week, but often don't have much strength for weights since I can't eat a lot of protein. I can't "just eat more" because if I don't wait until I'm hungry to eat (at least 3.5 hours after the last meal), I have the same problems, and gorging on carbs doesn't help you gain muscle mass. Believe me, I've tried.

I've had general health/blood tests done and they found nothing abnormal. They said I may have some form of IBS (though my bowel movements are normal), but that didn't help me much. I thought it may be my liver, but I did searches on liver problems and I don't seem to have the symptoms listed (I very rarely have diarreah, don't have yellowish skin or pain in my abdomen, etc.).

I've been to about 5 doctors over the last 15 years and none of them knew what to tell me. None of them were specialists. One alternative practitioner told me 13 years ago that I had leaky gut and candida. I've eaten such a clean diet since then that I'd be surprised if that was still the case, but maybe it's possible. If you don't know what to tell me, can you tell me what kind of specialist I should look for? What kind of doctor deals with the digestion of protein and fat? I need help from someone who is willing to admit that Acutane may have done damage to my body. If that's not the problem, I need someone who will look at the symptoms and help me find the cause, not just say "well, avoid fat." I'm tired of looking ill and tired. I live in Ft. Lauderdale FL and have United Health Golden Rule insurance. Thank you. Stephen