Thanks for your query.
You should not be worried but i think that you should do an ultrasound
to see your uterus and ovaries to rule out any of their pathology.
If you have done it and are normal you should a hormonal balance to see whats the matter.
For the back pain
this is may be due of irregular periods
or something unknown backpain (1 in 2 women have this pain ).Take pain killers such paracetamol
,ibuprofen and massage that zone .
Take care of your self