What should I do if I am having a miscarriage?

I think I’m having a miscarriage took a pregnancy test today but since yesterday I’ve had extremely painful abdominal pain and extremely bad back pain I’m having pains go down my legs and I’m extremely tired. This would be my 5th child and I’ve never experienced this with my other children and I’ve never had a miscarriage before so I can’t be certain. I felt so dizzy today I almost passed out. What do I do ? Do I go see a doctor or am I supposed to just let things run its course?