The irregularity of periods are mostly premenopausal, the other common cause like fibroid uterus
, FUH can be excluded by USG.
The foul smelling white discharge could be-
* perimenopausal-due to hormonal
*bacterial or viral STDs
*Forgain body-forgotten tampoon
The discharge not being blood tinged,no history of bleeding after sex so Its unlikely to be cancer- Please dont worry, get your investgations done with a free mind -to confirm the cause & start a proper T/t.