There are many ways to get motivated. I too get the feeling pretty often that i am bored or cant keep up to my projects but there are ways to get back in track.
1-music (now thats up to you on what to listen and your music taste but listening makes you forget the feeling of time and so you can keep on painting/ working for hours.
2-have movies that you have already watched play in the backround, especially lotr!
No need to watch them, just keep listening as your memory goes on with the scenes.
3-Set goals. If you encounter the problem that after painting a mini you feel bored to move to the next one. Try setting goals at the beginning of a project. For example you are up in the mood to paint elves, dont pick one and starting painting and pick another one and so on. Try to set a goal like ''This week i will paint these 5 specific elves'' Your mind keeps on thinking your goal and wont let you easily stop at 3 or 4
4-Post your work in sites like this one, there is no better thing than to get feedback for your work even if its not the one you want to hear. Another glorious point to this hobby is that everyone, even if they dont like the result you are posting will simple give an advice in a friendly way, always keep that advice
5- Experiment as much as you can to personalize your armies. Try giving a unique touch to your painting and you will feel more motivated when working on a unique project.
I hope thats helpful.