Can't think of a theme for my C minor sonata, what to do?

I have had this block in my C minor sonata for months. I have the introduction down as I want it but I can't think of a first theme to come after the introduction. Thankfully I have about 6 months before Beethoven's birthday comes around. That's right, I am dedicating this piano sonata to Beethoven, the 1 major composer that reinspired me after a long composer hiatus and who keeps pushing me forward in my compositions. I was able to compose a Mozart style sonata in less than a month.

But with this C minor sonata, it has been about a month and I still can't figure out what to do for the first theme.

@Tortualex on Musescore.com has given me quite a few suggestions after I told him that I wanted to be innovative with this sonata like how Beethoven was innovative more than 2 centuries before. One of them was to have it have 3 themes instead of your typical 2 themed sonata. In particular he suggested that I have this harmonic structure to my themes:

First theme in C minor
Second theme in G phrygian(which would have the same notes as C minor but have the tonic chord be G minor)
Third theme in G major

He said that with those 3 themes, I will have a lot of thematic material to have my sonata be more than 7 minutes long and still be interesting. He then suggested that I break more rules when I get to the recapitulation. Specifically that I make the second theme be in G major and use that G major as a secondary dominant to C minor(this though confuses me. Is he suggesting that I use the Locrian mode as the primary dominant instead of G major? Or is he suggesting that I have the third theme in G phrygian and use the minor dominant as the primary dominant?). Then afterwards he suggested having a second development followed by a true recapitulation. 

That would definitely be an expansion on your typical sonata form from the exposition having 3 themes instead of 2 to having a first recapitulation leading to a second development and then having a true recapitulation to the second theme being more modal than tonal.

I have gotten advice more related to symphonies but basically, one of the pieces of advice that I got for getting out of a composer's block was this:

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Don't think of the theme as being 1 long unbroken melody and accompaniment if you are getting stuck. Instead, think of a short little motive and then go all Beethoven's fifth on it, basing everything off of that 1 little motive and voila you have your theme without even thinking about it.

Now, I haven't been thinking much about my sonata since last month which I figured would relieve the composer's block with it because just not thinking about the piece for a while(sometimes just a few hours, sometimes a month or more) often relieves my composer's block. But it did no such thing for this C minor sonata. I'm still in as much of a composer's block as I was a month ago.

So should I go this motive route and base my first theme off of a short little motive instead of thinking of it as 1 long melody and accompaniment like I have been doing? If so, how will I know how workable a motive that I come up with is? Is there even such a thing as a motive being less workable than another?

Ah, composer's block—what would a composer be without it? I love how methodical you are in creating your music... wish I was that disciplined!

For me, finding melodies/motifs/themes is still like riding a wild bronco. I can't reallly tame it, I can only nudge it in the right direction. Find what inspires you—be it walking in the woods, spending time with friends, reading an epic story, watching a great film—and let it work its magic on you. Or think of an emotion you'd like to convey and see what music pops into your head. Even then, it's largely a trial-and-error process. I've often written hundreds of bars of material only to trash it all after a few days because the melodies just weren't doing anything for me.

The key to good melody writing isn't necessarily in finding an amazing melody; it's reallly in building variations around that melody to keep the listener's interest. There's so much one can vary when it comes to music! You can modulate, you can lower/raise the third (to make it major/minor), you can alter the tempo, alter the rhythm, alter the time signature—heck, you can even play the thing backwards! The possibilities are endless.

The bottom line is don't think; feel! Center your soul around an emotion and just start humming, see what comes to you. Even if it's not an instant melody, I bet it'll be something you can work with.

Happy composing!