Is Nystatin An Effective Medication For Armpit Rashes And A Possible Candida Infection In The Gut?

Question: I have a question about some fungal issues I've been having.

First off, I started taking probiotics a week ago. These probiotics have helped me a lot with depression and anxiety I was having. However, they don't appear to be addressing some physical issues I am having:

1. Eye floaters. I have a lot of random eye floaters which come and go and change. The eye doctor said my eyes are fine after an examination.
2. Armpit rashes. I used Lamisil which worked but the rashes keep coming back. I thought this was my deodorant so I switched deodorants 3 times and it still happens.
3. Oral thrush. The doctor noticed I have oral thrush on the back of my tongue and just prescribed me Nystatin to take 5ml 4 times a day.

I have greatly reduced sugar from my diet and am eating fairly healthy. I am 6'3, around 190lbs, and workout frequently as well. I read alot about these "candida diets" but a lot of people are saying that diet alone wasn't enough to get rid of it.

My questions are:

- will the Nystatin help with the armpit rashes and possible candida in my gut?
- should I go back to the doctor and ask for a more systematic anti-fungal medication?
- does it sound like I have a big fungus issue or bad candida overgrowth?
- how can I get all of this under control once and for all?