Is It Ok To Break Course Of Tablets And Continue Later?

Hi I am Swati.25 year old. my weight is 66 kgs and height is 5.3 . Recently had an urine infection doctor prescribed me Martifur 100 mg, 3 tablets day for 5 days. I could not finish the course in 5 days and still left with three tablets after 8 days. Wanted to know if i have the rest of them now, will it make any difference? Also i have a very severe allergy on my right hand ( arms ) - upper back side, which came to my notice yesterday only. Does the tablet has any side effects?