Hi. First of all that was an incredibly brave post to put up, and it does show how important this is to you and that you would be a great mum.
My advise would be to hold off until you are married (bit old fashioned I know), but it will give you a chance to get used to the diagnosis, your medication and perhaps get a counsellor you trust so you have alternatives to the medication.
Do your research well to understand the true risks to you and your baby. Talk to your doctor and find those forums to see what it has meant to and for others.
Build up a support network of friends and family. Will you have someone to look after the baby if you need a break or a chance to regroup?
Have a plan incase you are unlucky enough to get PPD (as people have said, there's no guarentee you will).
I think if you focus on stability (home, relationship, support, health) and being prepared (forums, doctor, research, plans), there is no reason why you can't be a mum. And think how precious your child(ren) will feel knowing what mum and dad did just to prepare for TTC!