Im scare if im pregnant?!

Im 13 this year and i never had sex but i been masterbate myself OUSIDE my vagina, but i took some slippery thing from my vagina and rub the outside with it. The next morning, i feel some thing from my lower back on the right side hurt, i sleep during the afternoon nap (i never sleep in the afternoon before)!
There was this one time i dont wash my hand before madterbate myself.
I just end my period 2 weeks ago. But 2 or 3 weeks before my period i got these kind of blood discharge thing when i wiped after using the bathroom. If ended quick. Its was light though.
Here are questions i wanna ask!

1) am i pregnant?
2) can sperm crawl from one place to another? (There are also boys in my house you know,ex: my brother, my cousin…)
3) is it ok to be like that if youre irregular period?
4) ive been having headache and nausea when i lay down.( the headache probably because i play my ipad too much)

Help me please! I dont pay attention in class!
10points for best answer!

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