How were you diagnosed? By that, I mean which blood tests did you have for the doctor to arrive at his decision? What was the actual result?
The normal diagnostic blood test is called an HbA1c. This measures the amount of glucose in your blood, and because our red blood cells live on average for 2 to 3 months, the levels measured are a sort of average of your blood sugar levels over the past 2 to 3 months, weighted towards the last few weeks.
It is true that steroids do raise blood sugar levels, but without knowing which test you had, and what the level was, it is impossible for us to say it was the steroids that caused it, although it is possible to say they won't have helped.