It's horrible timing for me! My weight fluctuates between 151 and 154 in the summer months, and between 155 and 158 the rest of the year. I was up around 170-172 a few years ago, but eating smaller portions and getting more aerobic exercise has kept those pounds at bay.
3 lb fluctuation is normal. Added weight between even 151 and 157 from summer to winter is normal too. You usually eat more with cold weather.
When you weigh less, maybe 1-2 pound fluctuation, could it be before and after a poop?