should I nightwean?

DD is 17 months old, happy, healthy and still nurses quite often during the
day and night. She goes through spurts of wanting to eat solids and will
eat lots and at other times just picks. I've never fussed too much as I
know she's still growing well and getting a lot from me.
Only problem is we want to have another child. For a number of reasons we
had wanted to have them close together but at this rate who knows when I'll
get my period back. I have severe polycystic ovarian syndrome and was
originally told that I would probably never have kids. Well DD was
conceived the first time we decided to stop using contraception to see what
would happen, which could have just been a wonderful blessing, or could mean
that maybe it's not too hard for me to get pregant after all.
We co-sleep and I am quite fine with her nursing as much as she wants to in
the night, so it's not that I actually want to stop, but I'm wondering if I
should to increase my chances of getting a period back. Thing is, I might
be one of those women that don't get a period as long as I'm still nursing
even infrequently, plus what if I can't have another baby - I would be
depriving her for nothing. But on the other hand, if I am going to have
troubles having another kid surely I should be trying to get pregnant in
case it takes a while - or not??

I just don't know what to do - DH keeps saying I should wean her just
because she's too old to be nursing anyway (to which I keep explaining that
I want to for as long as she and I still enjoy it) but he doesn't really
mind, I think it's just a society thing.
So the answer for him is easy, but I'm just not sure.

Plus then there would actually be the logistics of night weaning. We plan
on cosleeping for a while yet - till she's ready for her own bed, so that
would make it difficult to wean her although I did read on the Sears site
some ways to go about it. But it involves a couple of weeks of miserable
nights, which I really don't want to subject any of us to when it might not
even make any difference.

Thoughts and advice would be greatly appreciated