Need Advice!

Hey, I'm a 168 cm 17F and I'm trying to lose weight. I am always bloated and constipated so my weight really varies from day to day, I'm muslim so Ramadan is coming up and I think of it as a perfect opportunity to lose the kilos I want to lose, I don't really know how to track my calories because I usually don't make my food myself so I can't really estimate a value.

My weight varies from 64 to 66 kilos. I know it isn't much, but my high-school graduation is coming up and I want to feel good about myself and this year I've been studying from home so absolutely no movement and no walks anymore, I do have a treadmill but i rarely use it but am willing to start.

Note: if there's a free app that could be useful, please do share it I need all the help I can get!

Thanks in advance to all of you who could help me!!