Spotting and pain, implantation?????

Katia
Hi ladies I'm going crazy!!! I need your help with something that im not exactly sure what it is. 
So Friday morning I started spotting with a brownish pinkish discharge that was only there when I wiped and only once! The next day Saturday I spotted again pinkish with small blood clots again only when I wiped and only once in the morning. Sunday the same thing as Saturday but this time with a bit bigger clots. Monday and today I had no spotting at all but this after noon I started having really bad right side pelvic pain that spread to my back. I was literally crying from the pain. Ladies what do you think it could be?? Is it implantation spotting and pain? Has this happened to any of you? Note: I've taken hpt and they've been negative.