Okay. I've been trying forever to gain weight all to absolutely no avail. I can eat an absolute ton of food and it will have no effect on my body weight whatsoever. I'm talking everything from pizza to cheeseburgers, French fries etc. I try to now avoid bad foods because of the correlation with skin problems such as acne but even when I was consuming 3500-4000+ calories I was seeing no weight increase. I've been trying to lower histamine levels because I feel like I have histadelia which I know makes it hard to gain weight but I need help here.
First things that come to mind is either hyperthyroidism or some form of malabsorption. More information would be useful such as do you run a slightly high body temperature? Do you have problems with diarrhea? Do you live in areas known for parasites or have some other potential exposure source (eating raw meats, pets, etc.)? How long has this been going on? Any occupational exposure to toxic substances? Are you diabetic? Have you been checked for malignancies?.......
I have suspected hyperthyroidism in the past but when I went to see a specialist she asked me how long have I had this weight gain issue and I told her ever since I could remember. She shot down hyperthyroidism and told me that if that were the case I would have gotten a thyroid storm by now. I do have bulging eyes and light sensitivity as well but she said there is no correlation when it comes to me. I didn't get any actual tests ran because she said iy would just be a waste of money for me.
I've always been severely underweight and have always found it impossible to gain and keep on both weight and muscle. I'm saying since I was like 5 I have always been super skinny and I'm just sick of it.
There are other symptoms that can be good indicators of hyperthyroidism including a slightly elevated body temperature and diarrhea. The bulging eyes along with the other symptoms you have already mentioned though really sounds like hyperthyroidism. Sounds like you need to find a different doctor.