IUD symptoms

Rachel • I'm just a girl living in this big ole world trying to figure shit out💕
I had my IUD inserted in November. I didn't have any issues with it, (1 string retracted into my uterus and then came back out and bleeding for 3 weeks at a time) until this week. I've gained 9lbs in 3 days. 
I'm on a high protein low carb diet, I'm trying to lose body fat for a bikini competition. I've never gained that much weight before so quickly. Has anyone else gained weight on the IUD? 
Also I have unprotected sex with my boyfriend on a regular but so far everything is fine. My period was supposed to come today but I tested and it was negative.. pregnant? Or is my body still adjusting to the IUD? Could I have a thyroid problem? 
Thanks ladies! 😘