Acne, underweight, weak immune system.

Hello. I am absolutely desperate for answers. I've seen dozens of doctors and specialists of all kinds and spent thousands of dollars, but nothing has helped. I suffer from sever cystic acne. I used to take antibiotics for it, and they helped pretty amazingly, but I became resistant. I also used to suffer from acid reflux and constipation which I used to take antacids and laxatives for, but I have resolved those symptoms naturally with Magnesium, probiotics, digestive enzymes, and stomach juice. However, the acne continues to go through ups and downs with NO pattern whatsoever. Not in relation to my menstrual cycle, my eating habits (which are very healthy), my stress levels, or any external products I use. It is very cystic, very deep under the skin, and all over my face, but rarely anywhere else on my body. I do not drink and have never smoked or used drugs. I also have had low blood pressure all my life, pale skin, generally low body temperature, and I've always been underweight wit