Is it possible to have symptoms of pregnancy 3-4 days after conception?

No, not possible: 3-4 days after conception, it is unlikely that there is any detectable levels of any pregnancy related hormones. It is also possible that the pregnancy has not even implanted into the uterus yet. That being said, if you have been trying to get pregnant and feel pregnant, then you must take a pregnancy test. It is possible that you are pregnant from the previous cycle!

Unlikely: It takes a couple of days after an act of unprotected intercourse for the pregnancy to implant into the lining of the uterus. And until that happens, production of the hormones of pregnancy aren't high enough to produce systemic symptoms that a woman would feel in her body. 7 - 10 days later, by all means. But a few days, unlikely.