I would recommend that you see your primary care doctor
. Regardless of what is causing it or if it is related to your metabolism -- the numerous infections are worrisome. This should be evaluated by your primary care doctor.
To answer your question -- metabolism is probably not related to your ability to fight disease. Your basal metabolic rate (or metabolism) is how much energy your body consumes while at rest. This is determined by your muscle mass and other genetic factors. We do know that people who are very thin(too skinny) -- live shorter than those of normal weight. Therefore, both low and high weight are bad for overall health. However, normal weight (regardless of metabolism) is relatively safe. Talk to your doctor about measuring your BMI (body mass index) to see if your weight is appropriate.
That being said, there are some disease that increase both your metabolism and your infection risk. For example, excess thyroid hormone can cause this. This is known as hyperthyroidism and also causes diarrhea
, feeling warm and hyperactivity.
There are many disease that decrease your immune system -- your system to fight infections. I would recommend that you discuss this with your primary doctor in order to best evaluate this. Good luck!