Bleeding through *TMI*

My periods have gotten super heavy since my son was born and seem to get heavier each month (this is my 4th PP). I’m now finding that my tampon string is becoming saturated with blood after about an hour of me putting a fresh one in, so I’m having to change it literally every hour, but the tampon itself is not saturated and could probably be used for another hour or two. I’m using medium flow, as because the tampon is still fairly ok when I remove it, the heavier flow ones really hurt to remove.

Any ideas why this is happening? I know for a fact I’m inserting it correctly but I can’t see how the blood is skipping the tampon and coming straight out.

Sorry for graphic tmi.