Brown spotting, no period

Ca
Hi all -  just wondering if anybody out there has had this same phenomenon. I just had my IUD removed a month ago, and all seemed well through the first half of my cycle. Then, for the last two weeks I've had the worst PMS of my life. Feeling sick, headaches, crying all the time, emotionally awful, fatigued, etc, and really sore boob. What always happened before my IUD is about a week of PMS, then some cramps two days before period, then morning of period my boobs are back to normal and I start right off with heavy bleeding. This time, I had light cramps like I expected two days before I was due to bleed, but then I started spotting brown and my boobs are still crazy sore! Just very light spotting, and all my PMS symptoms are still there.  I have never had spotting before a period before, so I don't know what to think.  
I even took a pregnancy test, but it was negative.
What are y'all's thoughts?