OK, if this is just a breathing through the mouth/underwater thing, a simple thing to do is fill the sink, or a large dishpan, with water, and breathe through your snorkel with your face submerged. 15 minutes every evening until it's no big deal.
On the other hand, you alluded to other issues:
"I am a very insecure person & have no confidence. I am sure I can do it I just wish I was more positive & could get past the negativity & psychological issues I have created myself."
Now, this is a very politically incorrect, and unpopular thing to say around here, but depending on how accurate your quoted words above are, you may not be emotionally suited for diving, or any other activity where your life can depend upon rapidly and calmly making and executing decisions under stressful conditions. Now, you may notice that this characterization of diving can also be applied to a lot of things we take for granted every day, like driving a car. The good news is that your emotional makeup is not set in stone; it can be changed. You should consider how you can become a more confident and secure person not just for diving, but for all the challenges in life that this nervousness may interfere with. Only you can determine how to do this. Some people go to a therapist, others turn to their religious faith, and many people find that some sort of "boot camp" type experience helps. Whatever approach works for you, make sure you do it in a way that doesn't put you or others at undue risk.
On the other hand, you alluded to other issues:
"I am a very insecure person & have no confidence. I am sure I can do it I just wish I was more positive & could get past the negativity & psychological issues I have created myself."
Now, this is a very politically incorrect, and unpopular thing to say around here, but depending on how accurate your quoted words above are, you may not be emotionally suited for diving, or any other activity where your life can depend upon rapidly and calmly making and executing decisions under stressful conditions. Now, you may notice that this characterization of diving can also be applied to a lot of things we take for granted every day, like driving a car. The good news is that your emotional makeup is not set in stone; it can be changed. You should consider how you can become a more confident and secure person not just for diving, but for all the challenges in life that this nervousness may interfere with. Only you can determine how to do this. Some people go to a therapist, others turn to their religious faith, and many people find that some sort of "boot camp" type experience helps. Whatever approach works for you, make sure you do it in a way that doesn't put you or others at undue risk.