As a dev, not a manager, what's the maximum number of projects you can handle at once?

I know it depends on the workload but wanna see how others do on average.

Literally fried up with so many projects put on my shoulders after the exodus from my company since they f-ed up bonuses and hikes.

Also, why does every manager think their project is The Priority one? Selfish assholes.

Does anyone here have experience working as a senior developer in a web Application development company with less than 15 employee's and having around 5 - 6 developers? can you tell me what are the roles and expectation of graduate developers in such company? I landed a job(my first job ever) in such a company and I am working on 4 customer facing projects at a time including one massive government project. lot of pressure!!