How to manage many things at once without stress

I wished I'd have such a pure project manager role, but I'm expected to also be doing product, writing stories and doing non-technical hands-on work. Devs program, I do the rest.

I'm really not sure what to do when there is nobody to delegate to. I prioritize harshly and get bym but it's no fun when I lack time to sort my to-do just to move blockers for others/projects out of the way.