Fluctuating weight?

Allison • 20 years old. This was unplanned but I am keeping baby and being a single mom
I weighed about 138 pre-pregnancy, now I am 12w6d and I keep gaining and losing weight. I weigh 140.1 today and last week I weighed 142.5. The week before that I weighted 140.2. Has anyone else experienced this before? And no I haven't vomiting or anything recently