I note your history with interest & trepidation.
At the outset, if both your boyfriend & you have had these STD's in the past & been treated, i would imagine wiser counsel will have prevailed by now. Please do practice safe sex
As to what this yellowish discharge could be, it could be any of the STD linked discharges or a simple fungal infection
with a secondary bacterial infection. Is there an odour to it? Perchance a 'fishy' odour?
If so, trichomoniasis
cannot be ruled out.
By best advice would be to consult a venereologist, treat both your partner & yourself; treat the fomits/underwear et al & practice safe sex from now on.
Good Luck & Godspeed..wish you a safe sexlife!
Dr Praveen Rodrigues MD