Doubt or short-term memory loss?

How do I separate between the 2 issues? According to the level of importance I attribute to a certain situation, doubting my actions is always the outcome. However, sometimes I cannot remember something recent and if I have actually done what should be done. An example to clarify:

After I finish a school exam, I have to sign beside my name to confirm that I've taken the exam. After signing, I immediately start to doubt whether I've signed or not. On rare occasions, I even completely forget or am unable to form a picture about the whole situation. So what do I do? I put a 'sign' on my notebook to confirm that I've signed, just a simple compulsion. That's definitely targeted to ease doubt. I am, however, worried if I am starting to develop memory issues related to OCD and not to normal functioning (I am excellent at memorizing 'productive', and not anxious, stuff).

Any thoughts?