Is it normal to get your period twice a month sometimes?

A 21 day cycle is short but not abnormally so.

See your GP if you are worried.

yes of course- periods Do Not go by Months- they go by Cycle >Days>
your body has No idea What a Month is

your cycle is from Day 1 of your period to Day ONE of the next period

so your cycle was 22 Days- within normal range

the >Average> cycle is 28 days but it can be shorter or longer by a few days

you are Fine

suggest you Learn what Cycles are

The menstrual cycle, which is counted from the first day of one period to the first day of the next,

isn't the same for every woman.

Menstrual flow might occur every 21 to 35 days and last two to seven days.

For the first few years after menstruation begins, long cycles are common. However, menstrual cycles tend to shorten and become more regular as you age.

Your menstrual cycle might be regular — about the same length every month — or somewhat irregular, and your period might be light or heavy, painful or pain-free, long or short, and still be considered normal. Within a broad range, "normal" is what's normal for you.
Keep in mind that use of certain types of contraception, such as extended-cycle birth control pills and intrauterine devices (IUDs), will alter your menstrual cycle. Talk to your health care provider about what to expect.
When you get close to menopause, your cycle might become irregular again. However, because the risk of uterine cancer increases as you age, discuss any irregular bleeding around menopause with your health care provider.

It depends on your age. Its pretty common in teenagers. Not so common after the 20s. Talk to your mom if you are still a teen. If you are older you could bring this up with your doc at the next visit. Its not a major health concern unless there is major bleeding. This problem is called an irregular period.