It's water soluble, so no accumulation, but you are likely getting some level of folate in that leafy-greens diet of yours. So my guess is that 1000 mcg is way too much for you. I mostly take 400 mcg (more if sick or stressed) and I am double whammy on MTHFR C677T.
If you read the side effects of Deplin, Metafolin, etc, they all say upset stomach. I haven't really looked into the why.
I'd chuck it, and then order a lower dose when you run out. Somewhere down the road, maybe retest your homocysteine to see if it goes up with lower folate.
And let us know if this turns out to be the problem. If it's any consolation, I'm going through the same thing. I've gone on a supplement fast, and now adding some back to see which one(s) are the culprit.