I'm lactose intolerant but my parents don't really care anymore?

So I was always really sick to my stomach and had to miss school alot. My doctor wasn't sure what was wrong with me until she told us for me to go a week or two with out any dairy products. We did and that cured me and I was labeled lactose intolerant. For a couple months my mom would buy me lactose free milk and other stuff so I wouldn't get sick but now shes stopped and I've gone back to being sick but I've just suffered through it because, now that I'm older, it's become a bigger deal if I lay out if school. I've also put on alot of weight and I've read that's because I can't digest dairy products right so my body has learned to store it so that I'm not in pain all the time. When I'm at the store I ask to get the store brand of lactose free milk but my mom says we don't have room for it. Is there a way to end lactose intolerance??? Like a shot or something???? My self esteem has been bad, I feel sick with zero energy all the time, I gained 30lbs in 6 months. I know to stay away from it but i the only breakfast food we hav is cereal, and I ate it plain for a year and it's awful!!!!