You need to unlock your wallet, and you need enough PIVX so that a stake becomes likely (over a thousand is a good start). Although after 2 months, I would think even a small amount will have staked at least once, so maybe your wallet is just locked?
I have 240 pivx and the wallet is unlocked and stacking but still no stack.
That is strange, although 240 is maybe not quite enough. Did you update your wallet to the latest? There was a mandatory update recently.
My wallet is updated to the most recent. I think you are right. It might not be enough to stack