Weight gain and headaches

I got my IUD out on March 4th. My husband and I decided to ttc. I got my period 3 days later, March 8th, for 4 days. Since about two weeks ago, I have been bloated, nauseaus and headaches everyday! I've taken two pregnancy tests and they have both been negative. I don't know if it's too soon, I could possibly be pregnant, but could it be my body getting used to being off birth control? The IUD does not produce hormones so I was told by my doctor that my body should go right back to normal. Any other ideas?