Hi Meli!
Unfortunately i don't know if it's weak O or not. Even tho i've read that soy is not recommended to women who are regular or who O on their own, women still take it to get stronger O. It might and might not mess up your cycle, the only way to find out is to try it yourself, since all women are different.
If i was in your shoes i would try it for one cycle and see what would happen. If it will mess up your cycle then don't take it anymore after that.
Since you spot in your LP then i think natural progesterone cream would be good for you, if i remember right then spotting in your LP meant LP defect. This can make it harder for you to get pregnant. I used progesterone cream to bring on my period. I was spotting everyday for 3 months or so. Now i get my period with no help and i do have some super light spotting only around O time.
First time i took soy was CD1-5, 160,160,200,160,200 (first 200mg gave me a headache so i chickened out and took 160mg the next day lol ) didn't get my bfp cos i think my BD timing wasn't the best.
This is my second cycle on soy and this time i took CD2-6 and 160mg everyday. They do say to start with low dose but i was desperate for a baby