Pregnancy Scare

Okay, I have the implant in my arm but I'm still a worry wart. Me and my boyfriend had sex on our anniversary at the end of November with no condom. He didn't cum inside of me but I'm still scared because I just recently lost like a lot of weight randomly and I heard you can lose weight when you are pregnant in the first trimester. But I did gain weight on my birth control. So what does this mean??