This is embarrassing

[Lou]

Hi, I'm quite curious and embarrassed by my case. I would usually go to a dentist but I'm quite low on cash and won't afford one for months.
The last time I visited a hygienist was 5 months ago.
I used to wear braces and once I took them off I noticed this green patch between my teeth.
When I went to the doctor (5 months ago) he cleaned my teeth, and took care of the patch.
Soon after I would feel this "textures on my teeth from the inside and sometimes on the outside.
I can take off this texture by rubbing my teeth with a tissue.
But it would form soon after.
I brush and floss regularly.
I don't drink alcohol, and I don't drink soft drinks.
I don't smoke neither and my food is moderately healthy and balanced.
What's happening??? Because when I don't brush my teeth for one night, the next day they would be completely yellow?????????
Does this happen to everyone? Do teeth get easily off color?
There's also some brown spots?? I can sometimes rub/brush them out

 

[Lou]

I would be very grateful if you can just tell me the name of the disease or impairment that I have if you don't know any treatment or just guide me telling me where to start thank you