First, do not aerate now that primary fermentation is underway/mostly completed. It will probably lead to off-flavours in the beer (particularly since it is likely you will want to age/store it for a long period of time).
Second, you really do need to rely on your hydrometer readings to get any meaningful information about your fermentation. Rates/amounts of bubbling from the airlock provide only the coarsest level of information about degree of fermentation.
Given that it is an extract batch, you can estimate the OG relatively precisely. So it is not too late to obtain your current SG now. I suggest doing it. If it reveals that your fermentation is not complete (i.e., poor attenuation), you have two options:
1. Attempt to rouse the yeast from the bottom of the fermenter by gently stirring or shaking the carboy (probably will do little for a high gravity beer), or
2. Pitch some more healthy yeast.
I suggest trying option 1 first (nothing to lose, really, if you are very careful about not aerating the beer). If that doesn't work, you will have to pitch some more yeast to get the gravity down.
Occasionally you hear people suggest adding champagne yeast or beano or something else to get fermentation going again, but you also hear of a lot of problems developing from this. So exercise some caution before you choose these sorts of solutions over fresh yeast.
Best of luck!