I do understand that you are anxious to know about your pregnancy
status as are many women who attempt pregnancy.
With the kind of history that you have, the possibility of a pregnancy cannot be ruled out but it is still early days. It is unlikely the symptoms of nausea, and dizziness
occur so early on if the pregnancy occurred this month.
A more likely diagnosis appears to be just simple indigestion
. A concomitant pregnancy may be there but the symptoms you are having are unlikely to be due to the pregnancy as the baby is still not even properly attached to the uterus to produce pregnancy symptoms.
Having a backache during periods is not uncommon and is due to some local hormones that contract the uterus. This is not something that you should worry about. If the pain is severe then a simple pain reliever like diclofenac
I would recommend that you get a urine pregnancy test done preferably using the first morning sample of urine 4-5 days after you miss your period to clear your doubts
Hope this answer helps you. Please feel free to ask any further queries that you may have.