first
WELCOME!
WE NEED MORE BRITS!

second.
i hope youve read the stickies around here.

third.
Preflop call is ok, if you think it will only be heads up. personally playing a hand like AQ out of position in the small blind i probably want to reraise here rather than just call
On the flop its a nice flop for you, top pair. Opp miniraised which is basically horrible preflop play but hey. So when you bet out of position into a pot you will automatically get raised imo anyway, especially if he has top pair (yes he may also have the flush) AJX flop is a funny one as fishies like to min raise AJ as they darent or cant raise it properly so we have to count that in and that we are beat already but its not necessarily the case here.
basically you got beat by a player in position here without really knowing the strength of his hand. A lot of players (like me are gona auto raise your bet here in positon just... well because i can!)
So.
possibly reraise preflop. Not essential but something to think on
dont bet out of position on this flop. Id personally check raise here. You have a strong top pair but no heart which means this pot really wants to end quickly. If opp then 3 bets you i think its a laydown. No need to get involved in a big pot out of position.
I think the key is preflop but that is open to interpretation, just one way to look at it