Weight Gain....

Hello! I'm 14.5 weeks pregnant, but I've only gained 1.5lbs in total. I had a healthy BMI of 20 to begin with. In the second and third month I was quite sick and lost a couple pounds but I am now holding at 1.5lbs above my start weight. Is anyone else experiencing this? I've been reading that I should have gained nearly 5lbs by now!