💡 Detailed Explanation
The correct choice is 'のに' (even though / despite). The grammar pattern '[Verb Plain Form] + のに' expresses that the outcome is contrary to expectation, often carrying a nuance of regret or complaint. Sentence translation: 'Even though I took medicine, my cold is not getting better.' 'から' and 'ので' express cause/reason ('because'), which would contradict the negative outcome. 'ても' (even if) would require the te-form ('飲んでも') rather than the past plain form ('飲んだのに').