It'll be very hard to pinpoint the source of the infection. Some useful tips that I wish I had followed -
Wear a mask that offers a good fit (should allow very little air to come through unfiltered).
Since you live in a pg, I'd recommend wearing a mask as soon as you step outside your house door (rather than wearing it once you step outside the building).
If possible, avoid travelling in public transport with lots of people in it (pretty much all public transport in Bangalore).
Don't get pressurized by society to behave in a certain way. Most people I know don't follow covid safety protocols properly and even go as far as painting the ones that do follow safety protocols as weirdos. Don't hesitate to do what you know is safe.
As I said, it's hard to know exactly where someone gets the virus from. For me, I most likely got infected because I didn't do what I've mentioned above.