There's no way to know when you became pregnant based on the information you've given. You became pregnant sometime between late December and late January. That's as close as you can get without an ultrasound.
Sorry.

Did you ever use protection during any of those times? When did you first experience morning sickness? Maybe talk to your obgyn.
As said, it's very difficult to say. Everyone woman's pregnancy is different.

you count 40 weeks from the first day of your last period. thats as accurate as you can hope for without a scan before 18 weeks