When motivation is a problem, it's a real problem.  The more motivation you have to act, the easier it is to do.  The same is true in reverse: the less motivation you have, the harder it is to do.  Instead of feeling like you're on a smooth downward coast, it's an uphill struggle.  There is however, some good news.

If you feel like there's something that you need to do, there is at least a small degree of motivation within you.

No motivation at all leads to no action at all.  That includes the thought of action.  If you're thinking about doing something and recognizing that it's something that you need to do, you just don't want to do it, then you do have at least a little motivation.  It's important to recognize this because this subtle change in perception will make it easier for you to get to the action stage.

Instead of telling yourself, "I need motivation", change your thought to "I need more motivation".

This simple change of phrase signals to your mind that you do have at least some motivation.  This gives you a sense that you aren't starting from the ground floor and helps you feel like maybe you're doing better than you thought.

With this newfound motivation, let's go about cultivating more.  First, get out a piece of paper and a pen.  We're about to spend some time exploring.

The first thing you need to ask yourself (and write) is, "Why do I want to do this?"  Whatever is a struggle to get going on, make a list of all the reasons what you need or want to do it in the first place.  Remember, in order for it to be plaguing you, there is some underlying reason why you feel like you should do it.  List everything you can think of, no matter how trivial.

Once you feel like you've exhausted this list, take some time to go over it.  How do you feel about these reasons?  Are they valid reasons?  Can you support them?  Can you justify them?  For the maximum effect of this exercise, write these feelings down.  Write things like, "If I don't do this, I'll feel really guilty" and "I feel like this is what my mother would want me to do" and "I feel like this would make me feel so alive".  Whatever you're feeling about the reasons, write it down.

After this simple exercise, your direction should be clear.

If your reasons aren't something that you can get behind, then just forget about whatever it is you've been struggling with.  It's obviously not worth it and it's not worth the mental space and anxiety.  Let it go.  On the other hand, listing out your reasons can make you feel totally lit up about the situation.  It can bring out all the good point and reasons why you really should go for it; it'll increase your motivation.

Boom.  Problem solved.