That's not easy... if the weather is ok then you should go up till the highest point, called Torre. From there down to Sabugueiro, Seia where you can take N17 till you find directions to Coimbra/Arganil/tábua to have access to IC6, you'll end by entering IP3 direction Coimbra, exit to A31 and then follow any sign to A13. It's the only way to reach Tomar still with sometime to visit Tomar.
If the weather is bad there's no point on going up to Torre. Return from the Pousada to Covilhã and take A23 direction Lisbon, you may have a stop at Castelo Branco. Exit A23 direction Tomar (close to Entroncamento/Atalaia) but take N110, no need to Take A13 to go to Tomar.
Why are you staying at Ourém? Just because of the Pousada? It would be much more interesting to stay at Tomar, that way you could take your time going down from Covilhã till Tomar.