Okay Well I was on the birth control Mirena but decided to switch to Nexplanon. I got them switched on the same day so there was so time in-between. My doctor told me to be careful while having intercourse wear protection for the next two weeks but said she doubted I would be able to get pregnant. Here I am 3 weeks later used no protection I'm scared I might be pregnant, I woke up this morning sick to my stomach like morning sickness which with my first child I never had. I haven't had a period and I'm not sure when I will actually get one because while I was on Mirena it was unpredictable.

It is possible to get pregnant while on birth control, No form of birth control is 100 percent effective.

Now you have to wait and see if you miss your next period or not. You can not tell from "signs"

Even with 2 or more forms of birth control, pregnancy is possible. The only form of birth control that's 100% effective is abstinence. So yes, you could be pregnant. Too many women to count get pregnant while using birth control. There are more than a few on this site alone that used 3 forms of birth control, all used correctly, and still got pregnant. One of them more than once.

So yes, pregnancy is possible.

Since you don't get a period because of the mirena, I would go by when you had sex. I'd wait at least 4 weeks after sex, then test using first morning urine. If that test is negative, wait another 2 weeks, then test again, or get a blood test done.

Good luck.