Whenever I comment on a question, I get a vote-up, expecting that my reputation has being increased, I find out that it hasn't. So my question is, is the vote-up given to comments only proving that it has been supported or its a bug or anything related
It's not a bug, comments do not contribute to reputation, nor can they cause the loss of it. From the help centre - What is reputation? How do I earn (and lose) it?:
You gain reputation when:
question is voted up: +5
answer is voted up: +10
answer is marked “accepted”: +15 (+2 to acceptor)
suggested edit is accepted: +2 (up to +1000 total per user)
bounty awarded to your answer: + full bounty amount
one of your answers is awarded a bounty automatically: + half of the bounty amount (see more details about how bounties work)
site association bonus: +100 on each site (awarded a maximum of one time per site)
The fact that comments can't be downvoted along with the fact that they are less permanent than answers are the reason why answering in comments is frowned upon all across SE and especially on Health.
Also from the help centre - comment everywhere:
What are comments?
Comments are temporary "Post-It" notes left on a question or answer. They can be up-voted (but not down-voted) and flagged, but do not generate reputation. There's no revision history, and when they are deleted they're gone for good.
In general, reputation and voting serve for the community to pick the best answers (sometimes the system works well although it is not perfect) and they add some fun to the process, but SE is predominantly about gathering knowledge, not reputation.