Could I be starting a real period?

I haven't taken a pill in like almost two weeks. I had withdrawal bleeding a few days after I stopped, it lasted like four days and then stopped. I had sex during after this time. Then I never started a new pack. So I haven't taken a pill since a week before I had sex. 
Now I'm getting back aches and cramps that kinda feel like period cramps but not really, mood swings and other symptoms that could be pregnancy symptoms but also could be period symptoms. 
Is it possible even though I just had my withdrawal bleeding that I could be starting a period? Or should I be concerned about pregnancy and take a test?

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