Given a kenalog (triamcinolone) injection for a skin condition. Dr mentioned it may affect my menstrual cycle (and it has) but didn't say for how long. Any ideas?

One cycle. The half life of kenalog (triamcinolone) is around a month (depending on where it is given - 88 minutes in the blood). Thus, 1-2 cycles should be disturbed at the most.
2-3 months at most. Due to the long duration of kenalog, (triamcinolone) it may take 60-90 days to taper down to pre-injection levels and a usual period again.