Weight gain at week 13

Has anyone not gained any weight? I was 116.4 at 5 weeks, 118 at 9 and now at 13 weeks I’m back to 116?

I don’t eat a lot, like one meal a day and maybe a few snacks, I get full too much to eat more than that( I’ve always been that way ). The baby was measuring absolutely fine at 11weeks . But I’m nervous that I’m not eating enough and haven’t gained enough weight for the baby to be healthy. The doctor told me the first trimester I would gain about 3lbs.