Always nauseous!

I'm sick to my stomach every single day. I'm not eating anything different. There's no way I'm pregnant. I am on birth control though. I was taking it for a couple years then switched to mornings instead of nights. I've been sick since then but I thought it would regulate by now and Id stop feeling sick. The sickness is a hardcore nauseous feeling, to the point of almost throwing up. Then after a half an hour or so, I get rid of a bunch of gas and it goes away kinda. So I don't know what to do. Has anyone else had this issue or know how to fix it? I don't wanna change my birth control. This one was working for me!