B6 shortened my LP the one month I tried so I stopped it immediately. The more I read the more I heard it gave the opposite effect to a lot of people. The one thing that actually worked for me was Lunaception (if you search on here you can read about it and what I did) My LP went from 7-8 days to a BFP the month I tried lunaception. That month I was supposed to see a fertility doctor as nothing was working to lengthen it and I wasn't getting pregnant. We're team green so no idea what the gender is until december!
With both my sons I had a super regular cycle of 28 days and O on day 14. For months I wasn't Ovulation until CD22 and my cycle length would still stay at 28 days. Lunaception helped bring O earlier and made LP longer (and trust me - I am the LAST person to ever believe in this type of stuff!