Ab's not showing? Either you're not actually eating under your caloric maintenance or you just have very stubborn fat deposition genetics.
Protein intake? It's generally pretty overstated, you can go half bodyweight(in lbs) in grams or 3/4 bodyweight in grams and it's very ideal. I've never liked protein powder because it bloated the fuck out of me.
Swimming is a very slow twitch form of exercise. Building muscle is done by creating microtears in your muscles and proper resistance training like weightlifting is much more suited than swimming, which would mostly fatigue your muscles.
I think you should calculate your calorie maintenance level online based on height and weight, calc your diet calories in/out, and go whichever direction suits your goals