The answer is simple : Do not have unprotected sex (4 times in the month) so you will not "need" i-pill 4 times in the month.
i-pill 4 times per month is certainly not healthy. If your boyfriend does not want to buy condoms, dump him.
You ask about your future pregnancies ? What about your health now and in the future? Well, you are already full of artificial hormones - and you will need a lot of time to get rid of them from your system. How will this excess of artificial hormones affect your health, in the future, you will see as the time comes.
It is not only your future pregnancy you need to worry about, artificial hormones can cause all sorts of very serious health problems, if misused. Without health, there is no healthy pregnancy, and fur sure no healthy baby in case that pregnancy one day occurs.
No, i-pill is not safe to be used 4 times in month for sure, if you continue with such practise, you will be in very serious trouble soon.