Hi Aleya,
I do not understand the reason behind to pursue SAP SD module, when you have worked altogether in a different area, which is HR.
Anybody can do any module, but the logic is:
You education --> Business process knowledge --> interest should be in sync.
If not, then the people may not like their jobs.
Please do not just look opportunities, every module has its own merits and demerits as far as opportunities are concerned.
Passing Certification is not a big deal. Even if you do not anything, if you spend 2 months of committed time on any Certification, you should be able to pass easily.
Hope this helps.
Kind Regards,
Ravi