What's the solution for my kid's irregular periods?

A brown spotting might be a sign of implantation bleeding, but it is hard to definitively identify without a medical examination. Please talk to your gynecologist

I understand that you are concerned that you could be pregnant after unprotected sex on May 19 following your period on April 25. Let me tell you this: yes, you can get pregnant as the sperm can stay alive in a woman’s body for several days. Take a pregnancy test if you miss your period, have nausea, or feel tenderness in your breasts. 

Based on the information given, you seem to have cycles lasting 31 days. Period length is different from person to person and it can be also be affected by many factors that are external such as stress, weight changes, and some medical conditions. It is recommended to see a gynecologist if you have any problems with your mens cycles

Some women experience light bleeding around their regular period time when they are pregnant. This is caused by something called implantation bleeding when a fertilized egg attaches to the uterus. If you are unsure, you can take a pregnancy test to confirm. 

Stress impacts your pe­riod in various ways. When stressed, hormone­s release that postpone­ menstruation or make blee­ding lighter. Spotting commonly happens under stre­ss too. Deep breaths, e­xercise, confiding in others - the­se relaxation methods he­lp manage tension, regulating cycle­s.