Should you be looking? I have heard many answers, some good, some bad.
I would like to offer you a simple three-legged stool approach.
Like this stool, if your position meets all three of these standards, then STAY.
If your position meets TWO of these standards, then CONSIDER LEAVING.
If your position meets ONE or NONE of these standards, then START LOOKING.
Standard #1: Are you happy in your work? This means different things to different people, so I won't create a list here, because different things make different people happy. But, people know if they're happy in their work. And, like you can't be sort of pregnant, you can't be sort of happy. Also. If you have to think about it, chances are, you're not.
Is your pay meeting or exceeding what your industry standard is for where you are located? Invest in yourself and do your homework here.
Is your company stable? Have there been layoffs? Does your gut tell you that something's not right with your company or position? If you feel these things, go with your gut.