I'm 28. normally my periods are light to moderate. i change about every 7-8 hours. its way heavier and i bleed through in about 4 hrs. is this normal?

Heavy period: There is some variation in periods. If this persists and you use >7 pads in 24 hours would seek attention in ER or urgent care . May be fibroid, polyp,medications like advil/ asa which are blood thinners, or variation which can happen due to stress. ww.mayoclinic.org/diseases-conditions/menorrhagia/basics/treatment/con-20021959