How can I fix irregular periods?

The probability of pregnancy from the situation you described was quite low because you took the necessary measures after the unprotected encounter. Although light bleeding might have been caused by the pill's side effects, like irregular bleeding, this is not a sign of pregnancy. This idolizes the truth that hormonal changes can cause such and such. It is common and does not mean you are pregnant. If you're worried, taking a pregnancy test can provide reassurance. 

Emergency contraception like Plan B can throw your cycle off whack because of all the hormones it contains. It should only be a few days late. And if it doesn’t show up within another week or two, and feel free to take that pregnancy test. 

There could be a delay in menstrual cycle because of many reasons like stress, hormonal problems and some medical conditions. Nevertheless, you had no protection thus pregnancy is always a possibility for you. A pregnancy test and a visit to the gynecologist will be necessary for proper evaluation. They help you in knowing what to do and also give medical advice.
 

Weight gain could be the reason for your heavy periods. It can lead to hormonal changes, increasing blood volume and resulting in heavier periods. This happens because fat cells produce estrogen, which affects the menstrual cycle. To help regulate your periods, try maintaining a healthy weight by incorporating a balanced diet and regular exercise into your routine.

The vagina is a muscular canal that can dilate and contract. It opens up during arousal for penetration by a penis, dildo, or fingers. If you have any worries about your vaginal health, visit a gynecologist.