Yes, I am afraid it is most likely a fake. The closest I can come is a coin of Menader.
The reason why I think it is a fake is the weight. This is the most condemning piece of evidence. A drachm should weigh around 2.4grams. A tetradrachm
should weigh around 9.7 grams. You coin is in between these weights, and as far as I can tell no coin was made around 6 grams.
Finally, the style is wrong for these coins, especially the reverse. Instead of be a solid figure of Pallas standing left, there should be lines that make up the figure instead of solid blocky objects. The bust is too crude for this coin, especially the eye.