I noticed 2 weeks before my menses my immunity falls and my skin tends to be dry and feel weaker. Is it normal?

Oh yes, that's normal. Happens to me too -- I get super tired on top of all my mood swings. I also get the worst body aches. Before and during your period, estrogen levels are in a jumble so dehydration does happen, hence the dry skin. The weakness is a very common symptom of pre-menstrual blues. My best friend would say, "our bodies are about to bleed out... of course we are tired" whenever her husband asks her why she is so weak and "lazy" during this period haha (#men). Rest well, get enough sleep and try to stay as positive as you can. This all, will pass.