Writer's Block, Creative Block, losing interest, lost the spark...whatever you call it or however it happens to you, it is a frustrating thing. Some people never get through it and just plain give up. Some forever, others for a few years, some for a few weeks or days.
First remember, we ALL go through something like this at some point in time. There is no shame in it. Just recognize it and find a way to push through it and get that spark back.
Second, you are NOT ALONE. At least, you don't have to be. There are many photographers and creative types out there that can help you find the right thing for you that will re-spark your interest.
What I've done in the past to help me is:
Find a personal project. I did Sceene In Windows, and am working on 8 Corners and delving into video production. You can even become a photojournalist, like I have with my Visual Ohio project. Visual Ohio has actually gotten me visibility, work, and licensing of some images. I just had a call the other day for use of an image I took at an event last year for that organizations media packet. I then shoot street photography for fun/practice.
Sometimes you just have to step back from it. By doing this, you'll find out what it is that really draws you to photography. You'll start to get the desire to shoot again and when you do, what subject and how you shoot it can point you into a direction that will rekindle your interest. Follow that path.
On the business side - find something that no one else offers - master it and sell like crazy. Around here there are lots of people doing themed shoots. Normally they are cosplay or steam punk themed shoots. If you have a few good locations in mind- these kinds of clients tend to have their own costumes and want nothing more than someone to accept and respect them. I'm working on offering a new product, which is something similar to a living storyboard. We get a client(s) who has a story they want to tell and we go through a whole series of images that resemble a movie storyboard. Can be real or imaginary...but the point is, no one in my area is offering it. Once I get that flow down and better video chops, I plan on offering that same storyboard concept, except in video format - like a 5-10 minute short.
You may need to find a new client base - corporate gigs are nice if you can get them, but I find that working with the same client for a long time, doing the same kinds of things can be very stifling on the creative side. Forget outside the box, they generally don't want you even getting close to the sides of the box!! As an artist - and yes, I definitely consider every one of us photographers as one - that kind of necessary but sometimes uninteresting work can lead to stagnation. For those reasons, I do my personal projects, where the only limiter is either self imposed rules or none at all. That is probably why I love street shooting so much. All that "unknown" in front of you, not knowing what might happen that day. Sometimes something special, other times - nothing at all. What you can do though, is that the experimentation and creativity bleed into the other client jobs.
Again, trust that you'll get out of the rut, even the deepest one eventually. You've got friends everywhere, lean on us and we'll help you get through it.