I have all of the sudden developed pressure in my left ear that feels like it needs to pop but won't, and it's causing a bit of dizziness.

Eustachian tube... It sounds like your eustachian tube might be blocked, preventing your ear from equalizing pressure on either side of your ear drum. This can happen when you have cold symptoms like congestion. Drinking extra fluids can sometimes help loosed things up to reopen the tube. Also chewing gum, sucking on candy or yawning helps.Lastly, Benadryl (diphenhydramine) or a nose spray like afrin can help open things up.