Hello,<br/><br/>1. I have got <b>a fever</b>. or I have got <b>a stomachache</b>.<br/><br/>Why an article has been used before the word "fever" and "stomachache"?<br/><br/>Are they countable nouns? But I feel they are just our feeling. <br/><br/>How can they be countable? Please explain it.