Pregnancy symptoms?

My last period was VERY light. I didn't have to use any kind of products because the bleeding was so slight. Since then my nipples have been sore, I've been extremely bloated, my back has been sore, I've been sleeping 12-16 hours a day because I've been so exhausted, I've had a horrid copper taste in my mouth I can't seem to get rid of, and I feel like I have to pee every 45 minutes. I've taken four different pregnancy tests all negative. Could I be pregnant and it just be too early?