Use the pill identifier on drugs.com
You can just type in the imprint and legitimate pictures will show up. Study the picture of the pill you are suppose to have very very carefully. Pharmaceutical manufacturing is extremely precise. So even the smallest difference would be a good indicator of whether you are taking the same pill you think you are taking. For example, if the picture indicates your pill should have rounded edges, and your pill has a sharp/embossed/raised edge, this could be an indicator of two things:
The pills you've obtained are not the legitimate pharmaceutical that you think you have,
Or, the manufacturer has recently changed their production process.