OK, it could be one of many many reasons.

For a start, if it has been cured then it wont be harsh, so more likely its not been cured. Do you take a hit and hold it down? So many people do this and proves they know absolutly NOTHING about smoking cannabis. Like it says on the home page under the dailyfactoid, THC is absorbed instantly by the lungs, and if you hold your hits in all your doing is killing youself because your coating the lungs with tar.

If you dont hold it in, it might be good weed, your just not experienced enough.

I say get some glass jars, and slow cure it yourself for about a month. If its still too harsh, then make brownies or just cook with it.