Please someone help me.

Pre • 6 losses, 1 rainbow baby & 1 stillborn
On Sunday I got a digital positive so today I got another digital to check my levels where going up and it said not pregnant, so I took a cheap one and I got two lines. I've had 4 miscarriages and two chemical pregnancies so I know all about them. I don't know why my digital said pregnant and 3 days later my digital said not pregnant. Has this happened to anyone else?