I've had my depo shot 3 months ago... and it's almost time to go back to refill it. I've been having lots of pregnancy symptoms

It is quite possible, although the depo shot is a great form of birth control, it isn't 100% guaranteed. Wouldn't hurt to test.

No form of birth control is 100%. I personally know 2 women that got pregnant on depo (that's people that I know in person, not online). It's not fail safe.

If you feel you may be pregnant, test using first morning urine. If the test is negative, wait 2 weeks then test again, or get a blood test done.

Are you on schedule for having the next injection? Even if you are slightly late for it, your doctor will have you take a pregnancy test before the next injection. On schedule or not, let them know your concerns and they will test before giving you the injection.