Derffie, breathing on scuba is a little different than breathing normally. Practice long, slow inhales and long, slow exhales. I start my students on this idea right away; I tell them 3 to 4 seconds for inhale and they should try for 30 second exhales. It takes practice, but your brain will adapt quickly and soon you'll be doing it instinctively.
Also, air consumption is directly related to how "busy" your brain is. The more your brain is working, the faster it will demand air. This is why divers, especially new divers, with cameras go through their air faster. The more you dive, the more comfortable your brain will get, and the better your air consumption will get.
If your air consumption hasn't improved by your 80th dive, it could indicate you're more anxious while diving than you should be at that stage. If this is the case, you should consider why this would be so. Additional training beyond the basic OW class can usually build confidence and help alleviate anxiety.