Cramping no period

I just had a baby in early December and my period started back in January. Now in February I'm late like 3 whole days late! I took 2 tests both were negative. But on yesterday I had a small spot of blood in my panties and thought that was my period but that's all it was.  I was just wondering did this happen to anyone else and were you actually pregnant? Only time I've ever missed a period was from being pregnant