Air, light, and heat break down THC over time, so if it was exposed to any of those since that time, it can break down.

Next time dry it out really well, and store in an airtight container. Personally, I store mine in mason jars and small jam jars with the seperate lid and rim, ensuring air tight. I have kept this ounce in there curing nearly a month, and it smells and looks so damn good after that time.

Any airtight container will do, but I prefer glass. Plastic containers I find give it a plastic-y kind of taste.