How can you make it "safer" when having intercourse to avoid pregnancy aside from using condom and withdrawal? Can we use calendar method? By the way I have irregular periods. Thanks!

You can use tracking your cycle on the calendar, but with irregular periods that can be difficult depending on how irregular they are. If you know when your periods usually come on, you can better predict when you might be the most fertile and avoid that time frame. Natural Family Planning works best, obviously, when someone is quite regular and will be able to notice changes during each cycle.
This takes a few cycles to best get an idea, but you may want to start watching for signs that your body is preparing for ovulation and see if you can start to track them: cervical discharge becomes more fluid, clear, and abundant usually a few days prior to ovulation and you can do self-exams to check for changes in cervical position and consistency.

There are the options of birth control pills, injections, implants, etc. as well, but if you prefer not to use, or can't use, hormone type birth control that will limit your choices.
One type of IUD could be used, but it not usually recommended for anyone who has not given birth already.
Diaphragm, cervical cap are two other possible choices.

There are other options as well and it can depend on where you live as to what may be available to you. You can speak with your doctor about methods that may be best for you... some do require your doctor's assistance in obtaining and placing.

There is no 100 percent safe method, in fact even using pills and condoms there is a small chance and does happen.

If you are sexually active you should always know it is a chance and not be sexually active unless you are ready for that to happen if it does.

But using another form of control with that would be best