First shot 5 days ago (1.5) and I'm not losing weight

I decided to start at 1.5 to minimize the side effects, and I've done really well. I've had very little food noise -amazing to get a break from it. I had no idea just how obsessed I was with food! And I've had moments of peace in a way that I haven't had in years. But, I'm very constipated (I know it is expected), and I've had one time of relief from that, but nothing else.

The problem is that I am gaining weight. I've gained 1.5lbs over the past 5 days. I am 5'4" 181. I eat really clean (veggies, rice, tofu, and lots of water, focusing on protein, fiber, and water). And I go on walks 2 times a day, and I'm getting back to the gym at least twice a week.

I know I have a lot of room to go up, and this probably isn't a big deal, but I can't help but worry. I'm 51 and have hypothyroidism, and I'm on some other meds that slow down weight loss. So, I have a lot working against me when it comes to losing weight.