Cramping

Hi guys. I'm 4 weeks pregnant calculation from my last menstrual period but actually almost 3 weeks according to my doctor. from the day my period was due which was 5 days ago.  I have been experiencing little cramps. It's all in my lower abdomen. its mild sometimes and today it's kind of stabbing like feeling. I'm worried. is it my uterus expanding or is there sth wrong? Everything I read says sth different who else is experiencing this at this stage?

i don't have many symptoms aside shortness of breath and fatigue. that's it. Shortn of breath is occasional.

i have also travelled by road about 3 times in a week. 3houra for each journey. The doctor says that should not be an issue. 

what are your experiences? im worried.