Ok, I have lot of recommendations, so be prepared. I hope you will find something you will love!
Dramas similar to Oh My Ghost:
Strong Woman Do Bong Soon- FL is played by the same actress and it's also romantic comedy and a little bit of fantasy (FL is extra strong), couple with great chemistry
W- Two Worlds-also fantasy and romance drama, hot ML and great music
The Master's Sun- story is similar to Oh My Ghost( FL can see ghosts ), great acting and romantic scenes
Dramas that involves college:
My ID Is Gangnam Beauty- this one is really touching and romantic, you will love it!
Cheese In the Trap- this one is a little bit more dramatic and realistic but addicting
Heartstrings- college and music drama