when do I stop pumping with a micro premmie now 5w old & very low supply?

CC
He takes 17ml feeds every 2 hours and I'm only milking a daily total of about 20ml.
I've tried everything to increase it. I'm on medication & I've seen lactation consultants, midwives, doctors etc. This is my established supply and it's unlikely to change.
 
I'm getting stressed seeing the tiny amounts I get that have to be syringed up. I'm stressed doing this so often, including double pumping twice in a row with firm breast compressions, the taking apart & washing of the attachments etc. It's so much work and energy for such a frustrating result.
 
I'll keep going a while longer because of course I want to do as much as I can. But when is enough enough?