For 5yrs my sister is having burning in vaginal area & heavy discharge. Several tests have been done from STDs to infections, no respite for her. Help.

Many reasons. There are several other conditions that can cause this feeling of burning and discharge. Occasionally, heavy discharge can be completely normal however the burning sensation may indicate another type of problem that requires a doctor to evaluate and treat.. This sounds similar to vulvodynia, or vaginal pain without any infection or trauma but you will need a doctor's evaluation to be sure.