For starters, you are using already 2 seconds delay inthe loop. I am sure you are going to loose many data between this time spent on waiting.

Please provide more info on the program at PC side. What is sending and at what rate?

Also == has to be replaced by = and the () are not needed here.

One recommendation would be to have the PC send a start character like : and PIC wait for this character and then grab the next one.

like this:
serin PORTA.3,T9600,[":"],B0

Also ged rid off the pause commands.

Ioannis