Could I be pregnant even though I'm on birth control!?

I've had Nexplanon for about 2 1/2 years. I seen my boyfriend way over a month ago and I was on my period. Since we live in different states we really didn't want to miss the chance to have sex so we took it to the shower and back to his room but my period wasn't heavy at all. I've never been more than 2-3 days late. So I didn't think anything of it at first. Now I'm 21 days late. I'm nauseous all the time. Everything I eat makes me so sick. I don't even want to eat at this point thanks to that. My boobs feel funny, heavy I'd say and they look way bigger than they usually do when I'm getting and/or have my period. I've been hoping to get my period but seriously it's been 21 days! Any thoughts? I know the chances are super low but has anyone experienced this and was actually pregnant!??