Hello Good Evening,
is a branded progestogen-only contraceptive, depot medroxyprogesterone acetate
(DMPA) long acting reversible hormonal contraceptive
birth control drug that is injected every 3 months, which have very low or nil failure rate.
Depo-Provera can affect menstrual bleeding.
In the first months of use "irregular or unpredictable bleeding or spotting, or rarely, heavy or continuous bleeding" can be reported.
So most probably your spotting is due to Depo shot, nothing like pregnancy
You can confirm by Urine pregnancy test after 5-7 days.
Dr. Naresh Jain.