Not sure what's going on?

So I usually start my period at the beginning of every month. This month I started 2 weeks late. Of course me and my boyfriend got scared and took a test. It was negative and I ended up started my period a few days after that. My cramps were also UNBEARABLE too. They were worse than they ever are. (I'm not on my period right now btw.) Wednesday night I started having back cramps and it felt like it does when I'm on my period so I was confuse. They eventually went away but then I started feeling sick. I felt sick Wednesday night, Thursday night and now I feel sick tonight too. I feel like I'm going to throw up and I keep having to go to the bathroom. Tonight my back has been hurting towards the middle and the bottom, just making it uncomfortable to even just lie down. I know this doesn't have much to do with this app but I am a little concerned!! Has this happened to anyone else before??