I'm only answering here because of your post on the depression forum. A doctor can check for this, but it's not so easy to find systemic candida -- I assume you mean an infection that has gotten into your organs. A doc will look at your symptoms, do a blood test, and if really thorough do a urine test and stool test as well. If you Google this you will get more authoritative sites staffed by professionals, which this is not. It's not that common to get this, though it is obviously very common to get repeated yeast infections that are not systemic, but it does happen. Two ways that some think promote systemic infections are letting infections go untreated for long periods of time and repeated courses of antifungal medications, which also can kill off the beneficial organisms that protect you from getting this type of infection. If you are getting repeat infections, lifestyle changes are a good idea. You won't find this with your doctor, but you will with natural practitioners who will counsel you on diet (fungus loves sugar, for example) and natural ways of treating it that if it works won't also kill off the good guys that protect you.
Hello~Paxiled has given you a very good answer.
I would see a reputable naturopathic physician, they seem to specialize in areas like this, I know mine did back home. They know of tests that conventional MD's don't, plus, they will be able to prescribe the correct nutrients and foods to eat or not eat.
On your own, I would cut out all sugars, and wheat and yeast, Candida seems to love these foods. I would also add a good, high potency pro-biotic. Oh, and as to supplements, the naturopath will tell you also, but get the ones that are yeast, wheat and rice free.