Ask HN: How to Manage Tasks?

I am a Software Engineer at small Startup. When things goes south, I always go in and help. But, later the issues become mine.

I am always fill up with tasks even though I finish up quite lots. The demand is higher than what I can finish up.

There is a Project Manager, I chat with them and it's not help as well. It's like they don't know how to manage as well!

In these kind of situations, how should I manage up my tasks?