I'm a 22 year old girl, I have not had sexual active the whole year of 2014, and I started having sex on the 3rd, 4th and 5th of January 2015, and I had sex twice on all threes days and it was unprotected.

My periods are sometimes irregular. My periods should be due on the 20th of this month. I want to know is it possible that I could fall pregnant easily since I wasn't active for a year? I eat a lot, because every time my stomach rumbles I eat, and I have pains in my stomach and also on my lower back which come and go. I just want to know if it could be possible that I could have conceived from the time I started having sex.

Yes it's possible, especially as it was UNprotected.
That's how it usually works.

Not having sex for an entire year does not increase your chances. Having unprotected sex does increase your chances. No you would not be hungry or having pains about 15 days after sex.

You may be pregnant, but now you have to wait and see if you miss your next period

Do you know how reproduction works? You have sex, there is a chance you are pregnant...so yes, you could be. Are you? Who knows.

Any time you have sex, even if it's been years since you had sex, or the first time you had sex, even if you use protection, pregnancy is possible.

I would highly suggest that you research how pregnancy happens before you continue having sex.

You had unprotected sex, so there's a very good chance of pregnancy. Now you'll have to wait and see if you miss your period. If you do, wait a week then test using first morning urine. If that test is negative try another test a week later. If that test is negative wait for your next period. If you miss it, test again or see a doctor for a blood test.

Of course you could get pregnant, after having sex, especially if you used no protection. Has nothing to do with having no sex for a year. Now you have to wait and see to verify whether you are or NOT.