What Causes Excess Weight Loss?

Im 23 years old and i have a 2 year old daughter im 5 foot 6 inches.My problem is i am getting skinnier and skinner everday i eat regularly so i dont know .i sleep alot during the day time and i go to bed very late at nights could that be the problem please help im not worried or stressed about anything im not breast feeding im not even sexually active i do masterbate alot tho please tell me why im getting so skinny even my vains are showing and my collar bones are just so deep since ive lost the weight