New motor... Belt problems

About a year ago I replaced the motor. Ever since, it has been one belt squeal after another. Drive belts have slipped off 3 times. Alternator died a few weeks ago and was replaced. Belts are back to squealing again. Battery & brake lights appear when I got on top of any gear. If I lug the gear, they don't come on. My mechanic is completely baffled. HHHHEEEEELLLLLLPPPPP!!!!!!