MacBook Air Trackpad seems harder to push all of a sudden

I agree with MacMikeInOk, that you should bring the Mac to an Apple Store or an AASP and have them look at it. reason being is that I have an older MacBook Pro that the trackpad started feeling like I needed to push a little harder. and then, in short order, the battery noticeably started swelling up. if that happens to you, you will need to get the battery serviced. that is something that you do not want to put off.

If you're near an Apple Store (or authorized service center) I'd take it in an let the techs take a look at it. If it's physically harder to push now, there's very little we can offer in the way of assistance.