Hello everyone, I've been lurking on these threads for a long time and I'm now in need of a bit of advice.
I'm 36, and thinking very seriously about donor conception and solo parenting. But I would like some fertility tests to know if it is a realistic option for me. For the past few years, I've had very variable periods, mostly light but occasionally heavy and cycle length has varied too, from 21 days to 75(!). GP thought I might have PCOS and a blood test showed a marker for this but I had an ultrasound and there were no cysts on my ovaries. I'm also wondering if I might be in peri-menopause but don't really have any other symptoms which would indicate this.
So basically I can't be certain if I'm ovulating, or how often. And I'm just wondering where I would start to try and find out more about whether I might have issues conceiving, either due to possible PCOS or anything else. Do I go to my GP? What tests do I ask for? Or would it be better to book a fertility test at a private clinic? What do they look for?
I know there are no guarantees or certainties, either with tests or the process of conception, but I just feel that if I am going to struggle to conceive I would rather know that and take it into account when making the final, huge, decision to have a child. I hope I've explained that OK, I've been thinking about all this for so long now I am starting to go round in circles. 
Thank you to anyone who read and made sense of all that. And good luck and best wishes to you all, whatever stage of the journey you are at!