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If you have been taking the pills regularly then chances of pregnancy are remote as they provide effective protection against pregnancy.But it is advisable not to switch over pills frequently as it can cause hormonal fluctuations in the body.It might be possible that the cramps whioch you are having are due to the pill intake as pain abdomen,bloating,nausea,headache are some common side effects associated with pill use and are present for initial few months.
If other than this you notice any unusual symptom then consider visiting a Gynaecologist for evaluation.
Take care!