Birth control spotting?

I’ve recently started taking the combination pill, I took it for three days starting on my period, then stopped because it made me really nauseous. I called my doctor and he gave me a lower dose a few days later, I took three then stopped again because it still made me nauseous and now I am not on anything. However, I am at the beginning of my fertile window and I saw brown sludge in my undies today, not like a period at all for me. I had been having mild cramps earlier today however not anymore and I was wondering is this normal? If it is, does anyone know why this happen? Thank you so much!