Really, there are no safe days unless you know exactly when you ovulate. You would need to buy an ovulation kit and use it for several months to find out when your fertile days are.
Not all women ovulate in the middle of their cycles. You might ovulate right before or right after your period. Many young women think they're safe during his time when they're not.
I recommend you or your boyfriend buy condoms and use them every single time you have sex. You can also see your Dr to get on birth control. This is a better option in my opinion because you may not have a condom with you or you could have a break or tear in the condom. This is kind of rare but it can happen.
If you don't want to see your family Dr or a gynecologist then I recommend a woman's clinic. Research ones that are in your town or city. Where ever you choose to g they will give you several options for birth control. A clinic will go off of your income. If you have no income you could get birth conrol for free.
I hope this information helped. Please don't have sex without some form of birth control.You can buy condoms most any where. They don't cost much. You can use them until you decide if you want to use another form of birth control.