Implantation bleeding?

My period was due on March 24th. I've taken 4 hpt and all were negative. I took the last one on my 12th day of being late and still it was negative. and then last night on my 16th day late, I started spotting light pink blood for a few minutes. Then when I woke up it was bright red and heavy for a little while then it stopped and it's back to spotting.  I've had steady cramps through the morning and I noticed there's some tissue/clots in the blood. Is this a miscarriage? Or just my my regular period being super weird? im not sure what to do, as this would be my first pregnancy.