Could I be pregnant? Please help!

The last time I had sex was on December 21. I have the mirena iud and we used a condom as well. I got the iud inserted 3 and a half months ago. I am currently 16 days late on my period and I have been lightly spotting on and off for a while. I have taken multiple pregnancy tests after I missed my period and all of them have come up negative but I have been gaining weight and I feel like I have to pee all the time. What could be going on with me? I’ve taken so many tests and they have all been negative so I just don’t know what to do. I’ve also been having cramps too like I am getting my period but I never bleed. Anything helps. Could I be pregnant?