For the cramps, you can put a hot water bottle wrapped in a cloth to stop any scalding, on your tummy or your back. This will help ease any cramping pain.
This question has been answered in your previous posts.
First off, you can NOT get pregnant by sitting on a toilet seat when someone has masturbated. Tell your brother that if he messes up the toilet seat, he should out or respect for other people using the toilet after him, should clean and wash the mess up.
The reason you are feeling movements in your stomach is due to wind.
Wind in the stomach and move about. You may be feeling your intestines and bowels working.
A lot of wind in the stomach and belly can be due to drinking a lot of gassy drinks like lemonades, eating lots of foods like sprouts, cabbage, eating with your mouth open, and gulping air in when you drink fluids.
To help your periods to settle, eat a healthy and well balanced diet with lots of fluids (water, milk). You need your milk and dairy as your bones are still forming and growing.
Cut out or cut down on all sugary drinks and foods, junk and processed foods. Processed foods are those that are in tins and ready made meals.
At the moment your body is still changing and hasn't settled down with regard to hormones and your periods. Eating a healthy and well balanced diet will help. Evening Primrose oil may also help you with regard to the heavy periods and any premenstrual symptoms like bloating and sore breasts.
You ARE a normal kid. Everyone at some point will feel some movement in their belly due to trapped wind.