What Causes Missing Periods, Spotting And Cramps?

I took my period 29th April and usually have a cycle of 30 to 33 days but i haven't had another period, i had brown staining about 4 days ago then some clear mucus i have also been having cramps and my lower back is getting sore. Is there a possiblity i could be pregnant i have been trying for at least 6 years. I am 34 years of age and do take medication everyday for fibromyalgia.