Masturbation, in itself, is perfectly normal, natural, and is not harmful. The age you started masturbating is younger than average probably, but not unusual. Your behaviour as a teenager is pretty common, again probably a bit more often than average but not unusual.
However, like many other things, it can become an addiction, and this seems to be happening in your case. You are using masturbation as a way to try and escape your stress and your work problems (just the same way other people might use alcohol, drugs, gambling, or sex), but it doesn't make the problems go away.
This may be as much to do with your problems coping with stress and trying to escape it, as it is to do with masturbation itself.
Masturbation doesn't cause permanent ED. However, men generally have a maximum number of times they can orgasm (unlike most women - that's not fair!), so I'm not surprised that you have problems getting an erection the day after you've masturbated 3 times or more. And recovering a day or two later would be normal too.
I would suggest rationing yourself to no more than one per day. Think of it as a treat you'll give yourself at the end of the day, rather than a way to escape your problems and stress in the middle of the day. Then you can enjoy it rather than worrying or feeling guilty about it.
Try to find some other way of coping with your work problems and stress.
As for the blister, I honestly don't know. I have had the occasional lump on the shaft of mine, which has always turned out to be a sort of acne spot / pimple, not sore but eventually I've squeezed pus out just like a pimple on the face, and it's all healed up. I'd leave it a week or so, if it hasn't gone away on it's own, or it gets bigger or sore, go and see a doctor.
You say it's a month since you had sex. I hope you have success in finding someone you can have a meaningful, sexual relationship with, and then you can put all your sexual energies into your relationship with them, rather than masturbation.