Iv got a tilted womb and get really bad back ache when im due on a period is this normal?

May be endometriosis. It is common to have cramps with you period. Some women will have backache or back pain as well. This may just be normal for you. Many women with endometriosis will have the same symptoms, for many of them the symptoms have a tendency to get worse with time. Either way, most women will have improvement with birth control pills and/or nsaid's like ibuprofen, aspirin, and aleve (naproxen).
See your doctor. To be safe see your doctor.