Well, 3 aircrafts is next to nothing, so you can't expect much.
I remember that I had around 2.000.000$ profit per game week after around 1-2 years game time (and that's still not much really). But then again, I am based at a rather small airport in Greece with around 5.000.000 pax a year. There were sufficent underserved routes to quickly expand, slots were cheap, and I grabbed tons of dirt cheap Viscounts which helped a lot. In comparison: Slots for 1 daily flight cost like 20.000$. That's nothing in comparison with 800.000$.
So yes, your problem is your base: High slot costs, heavy competition. You may be better off starting again elsewhere where you can experience a better expansion. Think of secondary airports which are not very common. Things like Alicante, Prague, Budapest, Bordeaux, Stuttgart, Belfast, Bergamo, Corfu, etc. Just naming European airports as I am not very familiar with airports elsewhere.