Shaking and wobbling while in idle and the service engine light is flashing

I have had my vehicle for four years. Several days ago went to leave and noticed the back end was looking low. When I was out shopping the service engine light came on the and the car began to shake and felt wobbly when in park and when idling. Felt like it was misfiring too. So I changed the spark plugs all six of them and the alternator. Went to start car but battery was dead. Jumped car but had it tested and the battery was dead so bought a new battery. Car is still continues to shake a wobble service engine light is still flashing.