could just be shit weed, or like you say probally harvested too early or it could be you'r mind playing tricks. i once bought an oz of hash which on the first smoke of it i was questioning if it was any good or not and kept thinking it was shit i thought it looked a weird color and this made me question it as you allways do on the first one, i couldn't get stoned on it so basically i went stupid with it and started to waste it, it wasn't untill i was down to my last few joints that a mate came round i offerd him my hash to skin up and told him it was shit so use loads, 10 mins later he's telling me i'm out of order and he is well and truely stoned, after seeing this i got shitfaced and realised that it was some really good shit,but sadly by then it was nealy all gone lol.the mind is a powerful tool and if there is a bit of uncertainty it can greatly exsagerate it. get a mate to try it.