1. Food prices rise sharply in Egypt.

(What is the meaning of 'sharply' here?

2. Sometimes be happy.
3. Be sometimes happy.
4. Be happy sometimes.
(Can we use thises sentences? Which one is common?)

2 answers

prices rise a lot quickly

4 is all right. 2 and 3 do not sound right.
Damon is right about 2 and 3.

It's the placement of the adverb. In English, they usually are better when placed after the verb. Not always, but usually.