I had unprotected sex with my boyfriend 3 times but he didn't ejaculate inside me... (what is the concept of precum?) But I'm worried can I get pregnant it was my 8th day after my periods end?

And can I get pregnant after unprotected sex during my periods if my boyfriend came inside... Please help
And what is the min. time when you can do pregnancy test?

Anytime you have intercourse pregnancy is a possibility. There are plenty of sperm in the early fluids to cause pregnancy if you are near ovulation time.

You are now playing the waiting game. You have to wait to see if your next period comes as expected. If not, wait about 2 weeks after it is due and take a test using first morning urine following the directions on the box exactly.

Is there any other way to avoid pregnancy now...

Not at this point.

Pregnancy can can happen anytime you have sex. It can also happen using birth control, or even multiple forms of birth control. The only way to avoid pregnancy entirely, is to avoid intercourse.

Agree, you can get pregnant anytime you have sex. He does not have to "finish" inside of you, the early fluids can contain enough sperm for pregnancy.
If you plan on having sex, you need to arrange at least 2 forms of both controls. None are 100 percent with condoms having a 3 to 18 percent chance of failure. But even with two methods pregnancy does still happen sometimes.

Maybe the time to worry about pregnancy is at the point you say no to Mr. Condom. Truthfully it's a little ridiculous to worry about it after you've had unprotected sex.

And get some sex education please!