As Winston is walking through the proles...

[alabamagirl]

..And there is a bombing a few streets away, who is the bomber? I was thinking that it could possibly be Big Brother, and not an enemy. Maybe by bombing his own Oceania; he is trying to keep fear within them. Am I overthinking this??

[Granny5]

I think you've got it exactly right. It was a way of controlling the population.

[The Atheist]

..And there is a bombing a few streets away, who is the bomber? I was thinking that it could possibly be Big Brother, and not an enemy. Maybe by bombing his own Oceania; he is trying to keep fear within them. Am I overthinking this??

Not at all, you're dead right. Even Winston needs Julia to think this out for him before he realises the probability of it.

The mere fact that the bombs always land in prole areas gives the truth to it - an enemy would target power structures, not proles.