Hello,
As far as I know, weight gain doesn’t necessarily stop your period, nor would it alone make it irregular, since [during adolescence] weight gain is actually normal [and actually forcing yourself to throw up isn’t necessarily the best thing for you, especially if you think you may be pregnant]. Stress can put your cycles all out of wack though…. Basically I’d give it another week, and if your period doesn’t come, I would recommend being tested at a doctor’s office since the tests there are usually more sensitive to pregnancy hormone levels.
let me know how things turn out 🙂