AJ offsuit and medium pocket pairs in the BB

[mike4bmp]

I alway raise with AJo and medium pairs (77, 88 and 99)in the BB if no one else has opened up the pot before me. However, I always seem to get popped on the flop when I find out someone limped in with AK in middle position...or someone doesn't raise with TT on the button. Is my play correct?
I know you shouldn't do anything ALL THE TIME in poker...but I figure if it does not seem like I am making a profitable play now (which is reflected in my records) then just checking with these hands shouldn't make a difference...? Not sure...
Could it be due to me playing in the lower limits? I am playing 3/6 and 4/8...
Could it be possible that my cards did not run at those specific times when I held those in the BB? (seems to coincidental)

[Kevroc]

position position position and opponent dependant....

vs weak tighties fine, otherwise why not check and if you flop top pair or set you are in business.