Help me out

Okay so ... every month my period would come on and i would be okay .... so my previous and new period is killing me ! everytime i would wear my sanitary pads i would get rashes on my external vagina & almost near my anus . It’s very painful . I do change my pad every 4 hrs . And i clean properly . I’m not understanding why I’m having rashes on my vagina !! What could be the problem ? And how can i get rid of it ? It hurts when my pad rubs against my rashes 😭.