What Causes Stomach Discomforts And Backache During Delay Of Periods?

I am aged 45 last cycle was on 19th apri l after that till date l have no periods. But from 19th onwards I have been experiencing symptoms like stomach discomforts, backache like my period coming but it did not come. I have no doubt of pregnancy. (I had a very regular period till Feb, then Mar I had 2 periods one in 15th and next was on 28th and then April it was on 19th )