I feel heavy in lower part of stomach and pain in breasts and nipple? I'm doing sex since last 15 days in every alternate day after my periods... so what are the chances?
And I do work on computer regularly by sitting 7 hours a day on personal computer, kindly help whether it is not good to continue the job if preganant?

There is no way to know if you are pregnant or just having premenstrual symptoms, even if they are unusual for you.
You can work at a computer 7 hours a day while pregnant. 30 years ago there were concerns about women working at terminals with CRT screens and higher miscarriage rates.
Healthy diet, no smoking or alcohol, prenatal vitamins, and a bit of exercise each day are what's important.

It would be too early for you to have any pregnancy symptoms if you are pregnant.

Sitting behind a computer is not a problem during pregnancy.

Women do most work while pregnant, this is not a issue at all.

But there is no way to tell 15 days after sex. I will assume you are trying to get pregnant, but the everyother day is really hurting it, you need to tract your ovulation dates by body temp, not onling charts ( if that is what you are doing)

There is no way to tell if pregnant, till you miss a period, and then you have to wait till 14 days after you miss period. Before you can test.

*** there is normally no signs of pregnancy this soon.