Was the wheel cylinder on the right rear changed? They sometimes leak at the boot.
The screeching makes me think your bearing is crap, despite being new. Pull the drum off and spin the wheel forward and backward. If you hear grinding, it's your bearing. PS your mechanic should know this!
Your car doesn't "burn" brake fluid--if it's low, it's leaked out somewhere, either during the repair process (which you'd expect the mechanic to notice and replace) or after (when you've just had all the brakes serviced? That's not good!). Either way, your mechanic is missing something he shouldn't.
Best advice is to find a new shop.