Melanoma or Medication?

I am a cancer patient. I just finished 4 rounds of cytoxan and adriamycin chemotherapy. I am starting taxol this friday. About a month ago I noticed a dark spot on my left fingernail. It is now dark brown and moving down my nail slightly. It is IN my nail not under it. I also developed the same looking patches on my tongue. Side effects of cytoxan can be darkening of the nails but can it be isolated to one nail or does it change all nails? Do you think this is from the chemo meds?