I am a 20 year old girl. I always had normal periods cycle. I am sexually active since the last one year and I have always had safe sex, even my boy friend is very particular about safe sex. My period cycle used to come on the teen dates but it slowly shifted to the end of the month i.e 27th/28th, I have had sexual intercourse about 10 days back and I haven't had any sexual intercourse for about 30 days before that. My periods are supposed to be on this 28th but I missed it. Its 30th today and me and my boyfriend are pretty worried about this thing. Could you please help on this.

Please tell us the method of birth control you use. 'Safe sex' isn't enough info.
Even the pill, patch, IUD, and tubal ligation have a tiny % of pregnancies happen! As for condoms and other kinds, they have a high failure rate.
Of course your day of the month moves. Very few women have a cycle that is consistent, and the months don't have the same number of days anyway. And as you age your cycle may change too.
You could be pregnant, you could not be. It's just too soon to know. (You did have sex in the time range that you might be most fertile, but that varies too.)
Buy some home tests and wait a week or two from now and start using them.
The stress of worrying about this can even delay or stop a period! You just can't know until a test shows as positive.

It is just too early to say, 2 days, is not "late" if you wait a week and still no period, then you are late.

1. no form of birth control is 100 percent, I will assume you are on the pill and using condoms if you say you are very careful. But if you are doing that it is still possible of course

2. If you have not seen your period in two weeks, do a pregnancy test using the very first urine of the morning as soon as you wake up

BUT>>> many women are late now and then, and other will just miss a period every so often. So it is hard to tell. Worry will not help