You mean late to ovulate, right? From what I understand, the time between your last period and when you O varies each cycle and can be affected by stress, illness, etc. it's your luteal phase (the time between when you O and when your next period starts, and I'm sure you've heard all this but I figured I'd say it in case) that is pretty much the same (give or take a day or two) every month. Have you read Taking Charge of Your Fertility by Toni Weschler? Such a great book and I never fully understood how my body worked until I read it.
Anyway, so you're trying for baby #6?!? That's so exciting!! If you don't mind me asking, how many months pp did it take for af to return? My little guy is 10 months, nursing throughout the day and night, and af has yet to return...which is fine, but we're thinking of trying for #2 in the next couple months, so I'm starting to wonder how long it might take.
My midwives did tell me about vitex, which is from the chaste berry plant and can be used to help get your cycles more regular. It's just a supplement that you can buy at any health food store. That and there were some teas you can drink but I can't remember them off the top of my head and I have a sleeping baby in my lap ;) If you're interested I can always post them here later :)

I know that every woman is different but it helps to know what others go thru so here is how my body works. :). We have 6 children for the first 4 af didn't return till I was completely done breast feeding and I got pregnant soon after. Maybe a month or two later.... With # 5 af came at 5 months pp & I still didn't get pregnant till 2 months after my daughter weaned. # 6 is 10 months and af just showed up 3 days ago :(. Lol. So we shall see! If it is the desire of your heart that you have another baby God knows & is faithful.... The Bible says if we delight ourselves in Him, He will give us the desires of our heart! Trust Him!