Help!!!!

I have the implant and I've had it for two years, but I'm about a month late on my period and I've had some symptoms: really sore nipples with bumps getting bigger, really bloated and crampy. I don't know if any of these are signs, I tested a week ago and got a negative, but I did it in the evening so I don't know if that would of had any effect on it? My lower stomach feels really hard and just plain weird, help!!