After wearing a particular innerwear my vagina became red, and swollen with cotton cheese discharge. Why?

Hello,

Welcome to icliniq.com.

I understand your problem. What you describe is a classic case of yeast infection of vagina extending up to your anus. You need oral antifungal tablets weekly for three weeks alone with local antifungal ointment. The condition is very much infectious, so I suggest you avoid any sexual contact for the time being. I also would suggest you wear cotton panties to prevent a recurrence. Your current undergarments need to be washed with antiseptic in combination to your usual detergent and needs to be sundried nicely to remove all traces of spores. If you can discard them, it would be wonderful. I hope this helps you.