I have a mild cold and my left ear is kind of blocked. What do I do?

Decongestant/Time. Perhaps you need some time. In the meanwhile, you may try some otc decongestants (you may have to ask the pharmacist and sign for them) or you may try 2-4 days of a nasal decongestant spray. Mucolytics (like mucinex) may help to thin secretions an drain your passages. Take in plenty of water and use a humidifier. If persistent, get seen.