Sugarlove, in the past I've also had a short LP. For some women, extra B6 seems to do the trick. If you take it, start with an extra 50mgs every day. If that doesn't work, you can up your dose to 100mgs. It isn't safe to take more than 200mgs or so a day. I tried this and it didn't really work for me. My acupuncturist recommended a bio-identical progesterone cream. I started using that from ovulation until AF or into my first trimester. It definitely helped me to lengthen my LP. Mine was 10 -11 days and I've lengthened it to 12 - 13 days. I use the Emerita Pro-Gest brand.
However, it sounds like the length of yours is ok, you are just spotting for 7 days of it. Have you had your progesterone checked? Before you do anything, you should get it checked and talk to your doctor about options. Good luck!