New Swimmer

Hi guys, I'm a new swimmer, not so new maybe. I learned swimming when I was a child but stopped swimming after partially learning breaststroke. After 15 years I'm back to swimming with bad skills. I'm obese and had slipped disk in my backbone before, so doctor advised me to swim and yoga. I'm very into swimming recently, i find it challenging and interesting. I do have a few questions and hope I get some advice/feedback from the relevant community. Hope you guys don't mind me asking. :) 1) when doing breaststroke, both of my legs float a lot (too easily) even when I'm breathing in air (i.e. head sticks out of water). It feels like my body is in a skydiving posture. I see that a lot of people have their legs sink a little when they their head stick out of water). I heard that obese or overweight people are more likely to float more. Is this true and is this the reason why my legs are floating a lot? No matter how hard I try, my legs just wouldn't sink too much (especially feet will stick out of water too). Maybe there are some mistakes? 2) one of my motivations for swimming is to lose excessive fats, so I'm counting calories. I don't feel too tired after swimming like my sister, my muscles don't feel sore like how i feel when doing gym, does that mean I didn't swim hard enough to burn enough calories? Sorry if my questions sound silly and thanks if you're helping me out! :) Sent from my iPhone using Tapatalk