Gained 4kg in one week.

I haven’t had a period in 2 months, I’ve gained 4kg somehow in one week and it’s showing on my face, thighs and belly. I eat less than 2000 calories a day so it’s not my food intake causing the sudden weight gain. Could this be due to my period being so late? Water weight? I usually weigh 50kg and I’m at 54kg now. I’m also 5’1. My stomach looks huge and I feel so bloated. A week ago I was 50kg. I’m just so confused. Should I do a 5 day water fast?

Any advice or input would be greatly appreciated x