Cycle length after birth control?

OK I stopped birth control in late May. I started keeping track of my cycles in July. I had a 53 day cycle, then a 47 day cycle, then a 38 day cycle, then a 34 day, then two 31 day cycles in a row. 31 days is the length of my normal cycle, so I was pumped thinking it was back on track. So fallowing my 31 day cycle I expected my period on March 7 but it hasnt come yet. I used ovulation strips several times, and they are always postive around day 14, which would have been Feb 18. Is it normal for a cycle to get longer after steadily growing shorter and then being normal for two cycles?? I dont know whether to think I could be pregnant or to think my cycle is just being wierd........