Question!!

I have been cramping for a week. I never track my periods or when I ovulate. My Apple Watch says my last period started April 7th and “fertile window” is the 15th-20th...we had sex 14th, 18th, and 20th. I know there’s something called implantation cramping...I don’t remember that happening when I was pregnant with our son. How long does the cramping last if it’s implantation, and when should I take a test..