Do I have to make a suggestion or can I just end turn?
From the rules here

As soon as you enter a room, make a suggestion.

It's very common in games rules to use the word 'may' when something is optional.  The rules use the word 'may' in other places.  This would mean that making a suggestion is compulsory on entering a room.
However you may not remain in a room on your next turn. (and thus make another suggestion)

You may make only one Suggestion after entering a particular room.  To
make your next Suggestion, you must either enter a different Room or,
sometime after your next turn remain in a particular Room.

Thats not how I was taught the game as a child and we just stayed in the same room making suggestions!  So I've learnt something new today.