Not gaining weight

I am 15 weeks today and lost about 6 pounds during my first trimester (I was a little overweight in the first place). I haven’t gained hardly any of that back. I am up two pounds, then down two. I am eating when I feel hungry and it isn’t necessarily always healthy food. I also don’t seem to look any bigger and my bump seems non existent. Should I be gaining more weight by now? Or at least seeing some sort of a bump?