How come I dont see results? Is my DI affecting it?

So I have recently started working out. a week ago i think. And i've been eating a lot healthier and cut out my sweets. But I still seem to be gaining weight. All I do is the elliptical for 45 minutes because i am pressed for time. I have Diabetes Insipidus and am taking desmopressin which helps me retain water to stay hydrated. For some reason I went down from 150 to 130 and back up to 138..(I'm 5'7"). Is this because when you workout you tend to retain more water, so it's adding on to what i currently have? Or what is it. It certainly can't be muscle because I haven't been working out that long. It's really frustrating. And it all seems to be in my stomach area, i used to have a flat stomach but not anymore and it all happened so quickly. Please tell me this isn't the freshman 15