Почему у меня не могут быть месячные, если я не беременна?

It's normal to have cycle length variations. Factors like stress affect cycle regularity. A 28-33 day cycle is still regular.. . See a doctor if bleeding is HEAVY or PAINFUL. 

It's difficult to determine the exact cause without further info.. Stomach aches can have various causes which are unrelated factors like stress or dietary changes. If you're concerned about pregnancy then you may take a pregnancy test for confirmation.

You did the right thing and took the emergency contraception pill. The little period blood you had may be due to your body getting used to the pill. Blame it on the pill, or do you think it’s a sign of pregnancy? Moreover, you should know that yet another headache is the most common side effect of the emergency contraceptive pill. If in doubt, take a pregnancy test after a couple of weeks. 

Urinary tract infections often occur when bacteria enter the bladder and vagina. You might feel pain when peeing, experience lower belly pain, and have the urge to pee frequently. It's important to drink plenty of water and avoid holding in your pee. Sometimes, antibiotics are needed to help treat the infection.

After the intercourse if you had periods in March, April, and May, on March 5th, it's unlikely that you're pregnant, as regular periods suggest otherwise.

Taking abortion pills can make you bleed a little but it is usual to have some bleeding. If the bleeding goes away quickly and you have only a small amount of bleeding after, it can mean that the abortion is done. Just chill out and see how you feel. If you have intense pain, fever, or heavy bleeding, go to the nearest hospital without delay. 

The pills you swallowed are supposed to terminate the pregnancy; however, this might not happen immediately. Sometimes you may go through cramps, bleed, or even pass out some tissues. It may take some hours or even days for all these to happen. Should it be that you are scared or maybe you are experiencing too much pain or bleeding heavily, please seek medical help as soon as possible.