I have a very similar story. After having low milk supply for my first, I was worried about my second so was weighing her every couple of days until she was 2 months old. At that point, she had been gaining consistently, a minimum of 4 oz per week (remember that as they get older, they gain less in a week!). I decided at that point to stop weighing her, to save my sanity. We were moving for the winter and quite busy but she continued to nurse every 2-3 hrs and was the happiest baby. 2 months later I thought I'd weigh her again because I had noticed a slight decrease in her pees. She had gained 2 ounces in 2 months!! PANIC!! So I called my good friend and LC in tears, worried that I'd harmed her. She gave me some good advice to get more into her (breast compressions while she's nursing and switching back and forth between breasts) but the best advice was: look at the big picture..... Is your baby happy? Have good output? Good muscle tone? Meeting milestones? These are the things that matter, weight is not everything. Every baby grows at different rates and may gain little in a couple of weeks then a pound in the next 2 wks (like my little girl). I've stopped weighing her incessantly again, and watch for her to tell me what she wants. She's 7 months old now, and still a happy baby, and I have no idea how much she weighs!! But she eats, and pees, and poops, and sits on her own. Trust your little girl, and your mama instinct!
I would stop weighing her so often. If she gains a little more one week and a little less another week, it's not a big deal. You're looking at an overall trend. Weigh her maybe every 2-4 weeks and if she goes a longer interval without gaining, then I'd get her checked out... but if she seems okay otherwise, she probably is. I subscribe to the cave mamma principle... if I were a cave mamma, and didn't own a scale, I'd evaluate how my baby was doing by how she presented overall, if she seemed healthy and happy and was eliminating.