How early can back pain be a symptom?

Ok so I'm 6 days late on my period. Been feeling slightly nauseous but might be nothing as it's not too bad. Also had a couple of pains in my breast but only like twice which I don't think is how it is as a symptom? I've also been having sort of a weird feeling in my stomach- similar to cramps, but again not strong or anything. But for the last 2 weeks I've had such bad back pain- like really bad, it's kept me up at night- but I'm not sure if thats a symptom of pregnancy this early on? I haven't done anything to hurt my back and can't think of an explanation. It seems to go sometimes but then comes back the next day. Can you get back pain as a symptom this early in pregnancy?