I have taken IUI treatment on 18th Mar. Doctor prescribed duphaston from 22nd to 30th Mar. But I forgot to take. Now I missed my periods as due date was on 5th. But HPT was negetive. Should I go for blood test . Am I pregnant?

When did you take the pregnancy test, you are about one week late at this point, which often does not allow for a correct HPT. Often you will need to be at least two week late to start testing. The test must or should be in the morning as soon as you wake up with the first urine of the morning. So best at this point, wait one week and do another test.
** or you may of course go to your doctor.

Also the late period could be from many other issues.

At this point your period may be late, and not missed. See what happens in a week, and take another HPT.