Losing weight without trying. : (.

So in April 29th i had measured i was having around 69.1-70.0 kg weight, i joined gym and started weight training, despite that i see i am having weight loss! As of today i am having thr lower end 66.8 and highest being 67.8, i am trying to have calorie surplus too and also taking whey, i feel my body width is reducing, idk why, m really worried :(. I do have stomach issues like mushy stool, my stool colour is light yellow, recently since a month i am having gas problems, eating medicines but no complete resolution, I am really scared :(. I feel nauseous at times, also my sleep is disturbed as well. My friends see my and say you've become so thin, my height is 5'7 and m M25. I am really scared about anything serious, I want to gain weight, around 73KG. But unable to, i track my calorie records too, it's around 2700kcal per day.. help me someone :(.