Can a pretty bad deviated septum cause constant post nasal drip?

Possibly yes. If the deviated septum contributes to sinusitis, then constant nasal drip may occur. Your history of allergies may also contribute to this. If the drainage should become purulent or bloody, you may benefit from antibiotics.
Post nasal drip. Post nasal drip is not caused by a deviated septum. Rather it is caused by allergic rhinitis. You can have your nose evaluated by a board certified otolaryngologist.
Typically no. Septal deviations create airway obstruction if there is associated allergies, you may experience enlargement of your turbinates which may then give you post nasal drip if you do have seasonal allergies many people will elect to try over the counter products like Claritin assuming you have no allergy to it.

Related Questions

Would post nasal drip from allergies and a deviated septum cause constant sticky clear mucus and occasional dark brown mucus with blood in it?

Maybe. The clear mucus is certainly consistent with allergic rhinitis. Deviated septum not involved with allergic symptoms. Occasional brown/blood may be small volume nosebleed tinging mucus or signs of sinus infection, both of which may involve the deviated septum to some degree. Read more...
No. Post nasal drip from allergies is common, and it can produce clear mucous. The deviated septum will not produce discharge. Someone should look to see if they can find the source of the bleeding. That is of concern. Read more...

Can having a deviated septum cause really bad post nasal drip? Anytime I have a runny nose, the snot will fall to my mouth and I gag on it.

It can contribute. Are your symptoms affecting always 1 side more than the other? Are your symptoms getting worse?it may be that you suffer from a different condition in top of your deviated septum? Have you tried anything OTC- nasal saline? Either way you will probably need an ENT eval. Read more...
Post nasal drip. Post nasal drip is not caused by a deviated septum. Rather it is caused by allergic rhinitis. You can have your nose evaluated by a board certified otolaryngologist. Read more...

Can having deviated septum cause bad post nasal drip? Anytime I have a runny nose, snot will fall to my mouth and gag on it. Ent said sinuses are good

Unlikely. A deviated septum does not usually cause severe post nasal drip. If you have already seen an ENT doctor and sinusitis has been ruled out, I would consult an allergist. The major symptom of a deviated nasal septum is difficulty breathing through the side of the nose where the septal cartilage is deviated. Read more...