The swimsuit you wear when you dive sometimes drains your energy as you dive. Do you wear something tight fitting, or do you go for the loose boxer style swim trunk?
If you do not wear a wet suit loose swimsuits create drag as you move through the water. Drag created by the swimsuit is usually light, and hardly noticeable, but when combined with other equipment, that friction effect adds up.
I rarely see women having any trouble with friction caused by their bathing suits because their suits usually adhere well to their bodies.
If you wear loose fitting swimsuits, you do not feel it until after your dive, and the tiredness sets in, but during your dive the extra effort in fighting this drag causes you to breathe harder, and makes you suck air faster.
With each new dive out it looks I add something in the way of accessories to my dive outfit, and most of them hang from my buoyancy control device (BCD) somewhere.
For instance, even on day dives with full sunlight I always have a dive light because I like to explore cavities in rock piles, holes in walls, or small caves in the reef. I'm curious to see what lurks inside those places.
I take many notes on my dives for the articles and books I write. Right now my BCD has two dive slates hanging on it.
Add accessories like that to the BCD, which by necessity already has your compass / depth gauge / air pressure / computer console, and octopus hanging from various points, and you're talking about a lot of friction drag.
Much of this equipment is necessary for life support, and you have no option but to hang it from your BCD. The goal to seek is to secure all that stuff as tightly as safety permits so none of it floats freely, and opposes your forward motion.
The important objective is streamlining your equipment and your body so you do not work hard at moving through the water. The more stuff hanging, the more you work.
And the more you work at moving through the water, even at depth, the faster you burn through your available air supply. Faster air consumption means shorter dive times, and that means you do not get to enjoy your favorite sport – scuba diving.