crazy weight gain in one month

When I found out I was pregnant (2 weeks past conception) I was 147 lbs (5 ft 10''''). I didn''t have much morning sickness so gained weight fine in first trimester. At last check up (3 weeks ago) Dr. said my weight gain was healthy/normal. Since then I have put on a ton of weight! 10 pounds in about a month, 4 in the last week alone. At 20 weeks 5 days I''m now 167! There''s only one baby, my first, a boy. Reason to worry?