No, for this you need a logic level FET. The one you have requires a 10V signal for it to fully close, you need one that is fully closed with a 5V signal.
Only use a P-Channel FET when you want to top switch, that is switch the positive supply. The better FETs are for switching the ground, known as bottom switching.
I would need to see a schematic to explain why what you did gave unexpected results, but it will not matter which order you place parts in a series circuit.
This sounds muddled as well as being wrong.
I would guess this is an illusion, because if you actually understood FETs then you would not be asking these questions.