have itchy skin-mainly in evenings and when wearing clothes. Rashes are small but sometimes look like little red lines or dots joined up.

Background: been on sertraline for 6/7 weeks. Monday- increased dose to 100mg from 50mg. Had itching a few days before but not bad at all just random but has got a lot worse after increased dose and returning to university.
Had a bad cold two months ago with green phlegm which went and then got sinusitis but now still have a cough here and there and gunge in the nose but don't feel ill.
Itch is mainly worse in the evening but doesn't wake me up in the night. Any idea what this is?