First reset reset the SMC and Pram:
SMC:
1. Turn off MacBook Air.
2. Connect the power adapter and plug it in.
3. On the LEFT side of the keyboard (Yes, the left side only), hold down Shift, Option and Control.
4. Press the power button.
5. Wait 5 seconds, then release all keys.
6. Push power button to turn your MacBook Air back on.
7. Login, let boot fully up then shutdown.
PRAM and NVRAM
1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.
Next you will need to do OS maintenance:
Download Onyx and basically run everything. Allow it to check Smart Status and Verify the startup disk (these will happen when you launch the app, you will be given a choice of allowing or canceling, do both the first time but you don't need to repeat).
Under cleaning, clean everything on all six tabs - go right to left, only reboot after you have done all.
Go back in and do all 3 maintenance scripts (daily, weekly, monthly) in the Maintenance section - Scripts tab, reboot.
Again go back into the app and rebuild everything in the Maintenance section - Rebuild tab and reboot. Let it sit for several hours as some caches like spotlight will take a while to rebuild.
All of the above will probably take several hours but it will be well worth it.
Also check the logs (apps>utilities>console, all messages) and look for any repeating errors or warnings.
If you find any errors in the log repeating post back and I will try and help out.