The reason for your soft penis is already with you and you have given the reasons as well and that is masturbation. Dude, you have told that sometimes you masturbate 12 times a weak then what’s the average per day?
This is really a hard one to solve. You are just 19 years and what you have done is just unexpected from anyone. And you have also faced the problem while having sex. I would suggest you to stop masturbating as soon as possible and give your penis a rest for some time. You should read Top 11 Myths About Masturbation Effect Sex Life
However, you should eat natural foods that are good for your penis health and supports enough to stay you fit and stronger during sex.
Further, you can take help of supplements as there are several of them in market. Also there are several foods that can help you in this situation. 10 Best Foods to Boost your Sexual Stamina and Energy to Satisfy your Partner