Commercial diver here
I suggest you to follow a basic apnea course, they learn you the right way to breathe.
I paid my basic apnea course like 50 euros for 2 hours and I learned A LOT during that course.
also
>>915608THIS, don't fucking dive alone, it may sound annoying to always find a dive buddy but thrust me, I've seen a lot of accident during my career because of people diving without a partner
The only divers that are allowed and SAFE to dive alone are commercial divers