C section question

Hi ladies, for those of you who have experience with c sections:

I am 12 days post c section and my bleeding basically stopped. I switched from disposable loose undies to regular high waisted undies and noticed my bleeding has started again and is red. I’m kind of freaked out because the packet says of bleeding ramps up in doing too much…but my activities haven’t changed, just the tighter undies. Is this normal? I don’t want to mess up my interior stitches or something.