What Causes Sore Breasts And Pain In Lower Back With Delayed Periods?

Hello My name is Nichole , Ive missed a week and a day of my depo shot and i has sex on the 8th day that i missed my shot. After sex i've been feeling sea sick , my breasts are tender and sore , my lower back and side hurts , and i feel like i have to vomit but nothing comes up. I also feel constipated. I didnt feel this way until after sex. Could I be pregnant? Please help!