Tamoxifin and birth control

I am forty seven years old, was diagnosised with breast cancer two and half years ago.  I was estrogen receptor positive, early stage, no lymph node involvement, stage 0- but had a large mass and had to have a masectomy.  I take tamoxifin (tamoxifen), and am still having pretty regular periods.
My question is- Do I need to take birth control precautions while on tamoxifin (tamoxifen)?  My oncologist said I shouldn't have to while on this medicine, but the gynecologist said there was a slight chance I could get pregnant and should try the new IUD or something else w/o estrogen base.  I really would love to avoid taking more medicine, but do not want to risk becoming pregnant.
What is your advice?

[Cleveland Clinic]

Dear jsweeney:  It is possible to become pregnant any time you may be ovulating.  If you are having periods, it is possible that you may also be ovulating.  In fact, tamoxifen may increase ovulation.  We would recommend that you use some form of birth control (no hormone based contraceptives).  

[Mel in LA]

Would you be willing to tell me the type of cancer you had and the specifics?  It may help me with my decision.  Hope you are cancer free and stay that way!Thanks.

[MiracleB]

I am 47 years old and was using the depo-provera injections for birth control until I was diagnosed with infiltrating ductile carcinoma. I was told that I needed to stop taking it becuase of the hormone factors. Other options were limited. Either an IUD or tubal ligation. At this stage in me and my husbands life...not wanting any children, but still able to, I have elected to have a tubal ligation. I was fortunate that my lump was very small so it was removed with a lumpectomy and 2 lymph nodes. Both came back negative for cancer.Radiation is still be recommended but I am getting an MRI of both breast to make sure nothing else is going on, so futher treatment including radiation is pending. It has only been 3 weeks since my surgery and need to heal up a little more before the MRI. I am wondering how your radiation treatments went, in regards to side affects and,  .