The most signifigent sign that a snake is starting to loose weight is when you can start to really see the spine. So if you can see a signifigent weight loss just by eye then your not in danger yet. However, BP's generally don't go off feed unless something is wrong. My snake eats all year round and has rarely gone off feed, and when she did it was because of something wrong with her conditions.
But the others are right in that they can go long periods of time without eating and be ok. So 7 weeks is really on the lower end of the scale as far as ur snake going off feed so don't get too scared yet. I would check your tank and see if something is off that is stressing your snake out.