If you are having bright red bleeding, that means that is active bleeding, and you should call your Dr.
Lochia has three stages :
Lochia Rubra: first few days usually dark red
Lochia Serousa: can be brownish/pinkish-/yellowish 1-3 weekish post-partum
Lochia Alba: White/yellowish last stage. (abnormal if greater than 6 weeks)
Mind you if you are exclusively breastfeeding you might go through these stages a lot faster. Also if you are exclusively feeding breast milk and feeding on demand, and not using artificial nipples it is possible but rare to get your period this early. Even more rare is to start your period and be this heavy, only 4 weeks post partum.
It is normal if you are breastfeeding to have a light flow and all of a sudden your flow gets heavy in the beginning weeks after delivery. But, yah, it is not within the normal range to be saturating more than 1 pad in 1 hour, 4 weeks post-partum, and if you are passing clots, or having foul smelling d/c those are all other symptoms to report.
If you don't want to go to your ER. at least call your MD during regular office hours. But if you are experiencing Light-headness, or feelings of weakness, or you're getting out of breath you might have lost a lot of blood, and your body is trying to compensate for that loss.
A lot of women who breastfed take dietary supplements/herbs. Some of these herbs can make you prone to bleeding.