Mrs. Ping.. sorry to hear the witch got you.
Yes, you can take vitamin B to help lengthen your LP. You shouldn't take B6 alone though, there's a huge thread on here that explain it all but basically if you don't take the B vits in equal portions you can actually become deficient in some of the other ones (and B12 deficiency is linked to miscarriage). It also helps you absorb better if you have them all together. Usually recommend taking a B-50 complex or a B-100 complex (the 50 and 100 refer to amount of each vitamin, its normal to have higher folic acid in the mix).
Got my blood drawn this morning ... should hear my progesterone levels this afternoon.