Weight loss plateaud

I’ve been on the diet since September last year (took a break for Christmas) and I’ve lost 15 kg which is great but, I got down to that weight at the beginning of this year and I’ve not lost anything else, I still eat the same meat and even started to workout but nothing changes. There are days where I wake up in the morning 145 and the next 147 and so on, I’m getting frustrated (not disheartened, I’m not gonna stop the diet) I don’t know what I’m doing wrong or maybe I’m not doing anything wrong and there’s something up with me. I wanna know peoples input and if anyone has gone through this or maybe has an idea. I thought I might have hypothyroidism but that’s something I’ll have to check. Thanks Also I’m 17, m, 5'10 if you’re curious

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