Is this healthy, fluctuation of my weight within a short amount of time?

I seem to be going between 150 and 120 and then back to 150 or so, within s short amount of time. I can't seem to keep the weight off and I don't want to be 150 even though technically for my height I should be (while I'm lead to believe I'm 5'8", the last time I measured myself I was 5'5", so I'm not really sure what to believe).

I need something that will help me keep the weight off!
Is this healthy, fluctuation of my weight within a short amount of time?
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