hi lisa
um, first, yeah i suggest getting some lube, you may not always need it, but i believe one should always HAVE it avail, just in case.
i recommend Astroglide.
second, as for the cause...could be lots of things, could be nothing.
in general, i wouldn't worry about it, but to be sure, ask your Gyno.
good luck, and mostly, don't stress about it
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- + - ° GiRLie GeeK ° - + - °
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Therell be days/When Ill stray/I may appear to be/Constantly out of reach/I give in to sin/Because I like to practise what I preach