Welcome to HCM.
Your red purple spot over the shaft of penis may be a sebaceous cyst or some other cystic swelling as you described it has a bubble like head. This type of painless swelling is not a medical emergency. If you feel like a nuisance you can remove the same by some surgical procedures. If it is just a discoloration, then it could be due to some drug allergy
(fixed drug eruption
Regarding the dry skin
, nasal bleeding
and thinning after some medication may be due to calamine
lotion or a steroid. If you are able to send the picture of the spot and details about your medication, I would be able to guide you better.