Your goals are definitely achievable, and the fluctuating nature of your issues suggests to me that your problem is one of erection quality. As Titleist suggested, try to limit the masturbation to begin with, then I would recommend starting with manual exercises. Work on the newbie routine for at least a few months, then branch out into devices if you find you’re still interested.
While you work on that, I would also highly recommend finding time to increase your activity level if it’s reasonable. Exercise prompts greater testosterone production, and can also be helpful if you are carrying any excess body fat. Extra weight increases estrogen production, and can have a negative impact on circulation. Lastly, take a multivitamin that’s high in zinc and magnesium, as they can also help with hormone levels and circulation. I’ve also found several references to vitamin D and erection quality, though I’m not sure if it’s been scientifically verified.
Do you have any other medical conditions such as hypertension or diabetes?
Starting Stats Jan 2019 - BPEL: 6.75", MSEG: 5.875"
Now - BPEL: 7.0625", MSEG: 6.25"