Dull ache at very bottom of back. symptoms?

period due in around 10 days time. having some cramp like twinges. Also a terrible dull ache at the very bottom of my back (also kind of twingey too) some pain in left and into the armpit. we had around ovulation and used the pre seed lubrication which is recommended for couples trying to conceive. i have never suffered from anything like back ache/pain before not even before my period.