Pregnancy weight

I've only gained two pounds .. I started off at 120. Then I dropped a pound to 119. Then I was 121, now I'm 122.. I weighed 125 last summer and then dropped five pounds but now I'm afraid I won't be able to gain weight for the baby or myself and you can see the difference in me. Is there any foods I should put into my diet that would help me gain weight? Or any exercises I can do that would help at least my legs and butt gain weight back? Any advice helps, thanks girls