Is omnacortil 10mg safe to take?

I got wisdom tooth extracted in August and was prescribed with Zerodol MR post which i had blood in stool for 5 days. 2 years ago when i 1st extracted i had same situation. After taking pause 500 it stopped. I took vaccine on October 1st. Now, i am having itchy skin, and as per diagnosis i have cholinergic urticaria on my back. i have been prescribed with omnacortil 10mg once daily for 5 days.. I am not sure if the cause was the vaccine or some allergy since in the past i used to have itching sensation right after i took a bath which would subside after 30 to 40 mins but i never developed rashes which only happened within the last 2 weeks i.e. after taking the vaccine. I would also like to mention that i had a bike accident 2 years back post which i have back pain occassionaly due to issues in my L5-S1. Sometimes i take Mvista TM for this. I just want to know whether it would be safe for me to take this medicine given my condition and history..Can there be any other kind of reactions?