2000 pontiac check engine light flashing idealing rough. Why all the sudden this

What is your question?

Sarted the car one morning it had just got colder that night than any other night and it started ideling rough like it had bad plug changed plugs same thing it makes a sound from the tail pipe like it is missing. This happend after i changed the antifreeze in it drove it 80 miles or more parked it and next morning started ideling rough and check engine light flashing when driving. Now it wont start. Pls help this is my life line to make sure im at work.

What makes this problem better or worse?

Nothing

How long has your 2000 Pontiac Sunfire had this problem?

Starting monday this week