I've had a cold for the past two weeks. My cough had cleared now its back with phlem. Do I need to see a doctor? Its always worst at nighta!

Yes... This could be due to bronchospasm which can occur when a bronchitis infection is resolving. You may need a bronchodilator inhaler as well as a steroid inhaler until the cough resolves completely so see your doctor.
May be sinusitis. If a cold persists more than a week it could be sinusitis. If you only have a cough and no fever or pain you can try saline nasal irrigations and drinking lots of water. If symptoms worsen see a doctor.