Are my calories too low?

Hi everyone! On Jan 1st I started a deficit in the hopes of losing fat and gaining muscle. For reference, I’m a 23 year old female, 164cm and currently 62ish kg. When I weighed myself at the start of this deficit I was 62.6kg, and today I weighed in at 62.3kg. I originally set my goal at 1200 cal and 100g protein, with the intention of losing 5-8kg. I’ve also been doing 10k steps and doing a workout (usually either gym, long run, or long walk) every day where I can. This seems like a lot of exercise, but last year I was getting 8k steps regularly and also doing some form of exercise (same as above) around 5 days a week, so it’s not that drastic of an increase. Obviously the deficit itself is quite large, but despite that I’ve only lost 0.3kg, which I know is still good but just less than I would expect with such a large deficit. I’ve also noticed that my sleep has been terrible and my resting heart rate has decreased from around 60 to 43bpm which worries me. Are these all signs my calories are too low? Can too low calories slow my weight loss? These are the only issues I’ve had so far, aside from that I’ve been hitting my protein and calories every day eating only whole foods, and have been EXTREMELY full and very energised. I’m thinking of raising my calories to 1400 and 125g protein. Any tips would be greatly appreciated. Thank you! 🙏

Edit: I’ve also been super accurate with the counting. I’ve been weighing all my food and counting it using my fitness pal. I cook every time myself and as I said it’s all whole foods so everything I buy from the shop is raw fruits, veggies and meat (aside from my yoghurt). I’ve even been using the exact type of fruit and veg (ie. calypso mango instead of just mango) and even been counting my oil spray and spices, so I know accuracy isn’t the issue here :)