after: adverb
shortly after, etc
After can be used in adverb phrases like shortly after, long after, a few days after, etc.
- We had oysters for supper. Shortly after, I began to feel ill.
In more exact expressions of time, later is more common.
- They started the job on the 16th and finished three weeks later.
after not used alone
After is not normally used alone as an adverb. Instead, we use other expressions like afterwards (AmE also afterward), then or after that.
- I’m going to do my exams, and afterwards I’m going to study medicine. (not
… and after, I’m going …)