a few things are possible. one is that you've simply become acclimated to Clen in general. Your tolerance may be higher than it was the first time you used it. If both products are actually pharma grade, then they should be essentially identical products. Neither should be underdosed, or overdosed.
Shakiness of hands should not be how you measure it's effectiveness anyway. Why have you decided this is the determining factor for whether or not the product is good?
Oh, and of course your dealer insists it's original. What else would you expect? If there's an authentication code on the box and the company does not authenticate this product, it would raise a red flag for me....
As for what to do: let's assume the worst case scenario here, and that would be that your product is underdosed. If this is the case, you can either use more of it, or use the same amount as you originally intended to, and potentially get less than ideal results. The latter would be my preference, but that's obviously up to you. You're participating in black market drug use. You have to understand that this is part of what you will have to expect moving forward. I highly doubt your drug dealer has a return policy, so you have to make the best of it.