flatulence, excess gas, burping

My partner has been eating bigger quantities of food and has been less active recently, and its starting to affect her when she goes to the toilet. she use to poop every day at least, and now its maybe every 2 or 3 days? and its smaller than before. She also has a lot of gas, she says shes never had so much gas before. She also burps alot too.

Do you think this is due to her metabolism slowing down? she is 19 years old of age, we dont know whats causing these changes, we can only think is due to her eating habits being different, as before she use to snack alot whereas now she has proper meals.

any help or advice?