After iud help!

  Looking for any help from experienced past IUD users! 

   I had a copper iud that dislodged itself last December. It was 2 myths shy from removal date. Oddly enough all 9 1/2 yrs that I had the iud I had horrible and multiple menstrals (unusual from ever before) before iud I had very normal periods....5-7 days, no cramping.  

 NOW... Since the removal I must say I've had no cramping and normal menstrals as in 28-30 day intervals, but they are only lasting 2-3 days. Also, I've had 4 pos preg test..... For the last 4 mths.... Only to follow up by another period and multiple negatives. I don't believe I'm pregnant but I don't understand what's going on. Plus I'm gaining weight and look pregnant but know I'm obviously not. Has anyone else had this experience?  Thanks in advance for any advice!