chances of pregnancy?

What are the chances of pregnancy? I take my pill at the same time (within an hour) each night and my partner wears condoms. 
We had sex one night 4 times and changed condoms each time. One of the times it felt really wet and the condom just felt really slippery so we freaked out and changed to another condom. 3 days later I felt nauseous and had frequent urination and started freaking out so my boyfriend had but all his condoms in the bin in the bathroom. So he filled them all up with water and there was no breaks in them. 
Do you think we are safe. We had sex on the last day of my period. 

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