Good work doing the Beach Lifeguard qualification. It’s pretty hard work. Concentrate on long, slow ‘S’ pulls focusing on the push past your thigh (most propulsion). Do lots of 8x50m on 1min descending and 4x100m on 2mins descending. It’ll go down but needs plenty of training. Don’t worry about tumble turns, they burn loads of energy unless you’re very good at them. Spend your time on decent technique and keep your head down to encourage your legs to stay higher in the water.
Speedo’s or jammers will make it a lot easier.
Where are you doing the qualification?