What form of IUD do you have? If it's the Mirena, what you've described is normal side effects. Overtime you can gain weight, it can make you tired, nauseated, headaches, backaches, bloating, breast changes/tenderness, etc etc. Even at 12 weeks pregnant a weight gain of 10-15 pounds is very unhealthy--it's close to half the total recommended weight.
You need to see a doctor to be tested, but as long as it's in place the odds of pregnancy are very low.
I had the same thing happen about 2 years ago. Turns out it was nothing. It was all n my head. I think ur ok if u've taken tests and they come out negative.
hCG pregnancy hormone should reach it's extremes at 12 weeks pregnancy and if you were really pregnant the test should be so positive by now...gaining weight ,stress ,hormone changes all are factors that may cause your period to be delayed all you can do at the mean time is to visit ur Dr a scan should be done bec at 12 weeks the fetus should be around 10 cm heart beat about 150 beats per minute ,good luck anyway tc !
you cant take a test too late i dont think as a friend of mine was 5 months when she discovered she was pregnant using a test.
Id recommend going to the doctors and discussing the symptoms. They may do a blood test.
Try doing a test in the morning.