On December 22nd I got my period n had sex jan5 then jan 19 I got my period then when febrary came along I missed periodwhen would have I got peegnant before after my period of yoof the 19 or before that

There's really no way to determine when you conceived. An ultrasound will give you a better guess, but it's still a guess.

Is this a question of paternity, is that why you're concerned about your conception date? If so, a DNA test after the baby is born, is your only option.

Good luck.

Unless it is a matter of paternity ( and you did not say it was) first it does not really matter.
But from even testing will only give you a estimate