Help! 6 weeks PP still no period?!

So I am 6 weeks PP and I still have had no period at all. I am not breastfeeding I have been having cramps, and 1 1/2 ago I had some spotting but that's it! I don't know what is going on. I have had unprotected sex but used pull out method. My cm is watery right now. I really thought I would have it by now. I have had 3 children you would think I would remember but I don't at all.. I can't start my bc until I have it and my ob did a pregnancy test it came up negative. So I don't know what to think am I freaking out about this? Or could I have gotten a negative on last Monday and I actually be pregnant? Has this happened to anyone else?