I'm really hoping I can finally get some opinions/help

MY ACNE STORY.

I had flawless skin until grade 9. I started getting a few pimples, then soon enough my entire forehead was covered in colourless bumps. Since it started I haven't had a day without tons of acne on my forehead. My entire family has never had acne. So I didn't really have anyone to get good advice from, which of course lead me to buying super harsh face scrubs/topical gels I didn't need. That made it SO MUCH WORSE, my entire face was dry all the time, it made my forehead red and definitely inflamed the pimples, making them bigger YAY! I had no idea it was making it worse so I kept doing that for years. I'm 19 now and started using Cetaphil moisturizing cleanser and moisturizer, although it hasn't cleared my acne it hasn't made it worse. I still have acne all over my forehead, I still haven't had a day of clear skin. For a long time I thought it was hormonal (because that's what every teenager thinks right?) but I only get bumps on my forehead and the occasional white head. Which leads me to believe it's because of my diet, I'm 5'6 and 115 pounds it's been really hard for me to gain weight. I can eat whatever I want and not gain a pound, my diet is horrible! I drink soda and coffee, everything I eat now is processed (I'm a broke uni student) I rarely drink water, horrible I know. I don't eat vegetables and It was the same way when I lived at home.

This is where I need help!

I've been looking into this theory for a few weeks and I've seen a lot of things I'm hoping is my cure to this never ending bullshit. The first time I read about "poor diet causing acne" was on a chinese face map. Having acne on my forehead supposably means I need to help my intestines. The solutions were sleep more and at a normal time, drink water, eat healthy foods and work out. I'm not doing any of those things so it started making sense. The causes were drinking soda, irregular sleeping, stressing out, processed foods. I'm doing all of those! I stress non stop because of acne, I don't have horrible skin it's definitely not the worst in the world but knowing I have hundreds of little bumps on my forehead at all times really stresses me out. Has anyone had this same problem? Have you fixed it? And i'd love peoples opinions on completely cutting sugar out of my diet drinking lots of water and working out will that solve my problem?