The profile on steroids.com for nandrolone does say it raises prolactin levels.
http://www.steroid.com/Nandrolone.php
Now as far as the effectiveness of tamoxifen goes:
Previous investigations of animal treated with a variety of classical antiestrogenic compounds such as tamoxifen and its derivatives have also shown little or no changes in the expression of estrogen and progesterone receptors in their mammary tissue after treatment [31].
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1940067/
And in a study about lowering prolactin levels.
In conclusion, the results of the present paper showed that tamoxifen reduced estrogen-stimulated prolactin levels in some, but not in other hormonal conditions and that these effects were not mediated by an inhibition of lactotroph cell growth.
http://www.ncbi.nlm.nih.gov/pubmed/8...?log$=activity
That's why I suggest a drug like cabergoline.