Need reassurance/advice!

So I'm very early in pregnancy (3w6d) and started the implantation bleeding yesterday. However the cramps that go along with it feel like menstrual cramps. I know that's fairly normal but everytime I start feeling them, I get scared AF is about to rear her ugly head and I'm going to lose the baby. How long did implantation cramping last for all you mommies out there? Any advice for how to calm the nerves when they start in again so I won't constantly be afraid that I'm about to miscarry this baby?!?!