Lactase is the best thing... and maybe only thing. If you have dairy, and take a lactase pill (like Lactaid), it provides the enzymes your body lacks to break down the lactose. If I've missed the window to take a pill, I try to just drink a lot of water to help it get out of my system faster :/

Most dairy food upset my stomach but the weird thing is yogurt is the only dairy food that doesn't upset my stomach but the rest of the dairy food are horrible on my stomach

I have found that drinking lots of water and eating something spongy like bread helps to make the symptoms better. Hope this helps!