Question about top two---400 NL

[JasonP530]

SB has 250 and is bad. SB has 200 and is bad. MP has 550 and is pretty tight(25/4). I have 450 and am on the button with AJs.

MP limps. MP+2 limps and I limp on the button with AJs. Sometimes I raise, but this time I elected just to see the flop cheaply.

Flop is J74 and 2 diamonds(I have hearts). All check to me, and I fire out a pot sized bet of $20. A lot of times in this spot I fire out the full pot, so I can see where people stand in an unraised pot. I would not like to bet half, and be checkraised by someone who thinks their hand is good. If someone calls, I can always check behind the turn if need be.

SB, BB and UTG all call. I thought that SB, and BB could be on draws, or have flopped 2 pairs(they would wait for the turn I believe). MP really had me a little worried, as his overcall there I thought was odd(wouldn't he have led a draw there?).

The turn is an ace, giving me top two. Now I am sure I am ahead of the BB and SB, and am willing to go broke to them if they flopped a set, but MP is still a ?. Checked to MP who fires out $45 into a $97 pot. I thought it was a strange bet(perhaps he had nut high diamonds and hit the ace), but I didnt want to give a cheap draw to the blinds, so I raised to $150. My plan at this point was to fold to a reraise by the MP, on the thought that he limped in, and played his hand like a set, and against his reraising range I am toast. In any event, he just calls.

The river is a Q(not of diamonds). He checks to me. I thought that if he didn't have enough to push the turn, unless he had AQ of diamonds, I was still ahead, so I decided to push for 300 more into a ~400 pot or so.

I wanted to get some feedback on my thought process throughout the hand. Obviously it turned out poorly, as he showed a set of 7's. Is there any way to play it differently? Should I check the river? Or was it just right?

Thanks,
Jason