A depot injection is usually given at the onset of the periodic menstrual bleed either on day 1 or 2. So if you had unprotected sex on day 3 of your cycle then you being in safe period when ovulation had not occurred , there are no chances of you getting pregnant.
However if given in the middle of the cycle ( which you havent specified) , then it must have been advised to you to follow barrier contraception for the whole month as protection from depot would take around 2-3 weeks to establish. So if you had sex in the fertile period then you may be pregnant.
You can confirm pregnancy or rule out presently with a serum beta hcg test which if found to have raised levels would confirm pregnancy. If negative then these symptoms experienced by you form a part of the premenstrual syndrome and you should be expecting your menses sooner.
I hope i have answered your query,
wishing you good health,
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.