Sometimes your period gets screwed up during the depo shot!! I doubt you're pregnant because normally with the depo you should be fine to not use a Condom but if you're really worried a test should be positive within 2 weeks or so after you had sex ....my bf and I used only the depo shot, no condoms, spermicide, etc. for 2 years and I never got pregnant, even after stopping the shot it took 10 months of not using any other protection and lots of sex to get pregnant with my Daughter lol.... The depo shot is notorious for taking a while after stopping it to get back your fertility!!! Id assume your symptoms are due to your period or maybe just hormones....I also missed my period a lot while on it but I would always feel crampy, get sore boobs, and sometimes spot during the time I was due for it though!! Good luck either way!!