Listening is crucial to learning the art of composing fugues. Bach is the best place to start when it comes to composing a fugue, but plenty of other composers have written admirable themes. Mendelssohn, Franck, Beethoven, Liszt and then there are 20th century fugue composers. Ives wrote a fugue (in 4 keys IIRC), Barber wrote an awesome one in his Piano Sonata, Shostakovich, wrote 24 preludes and fugues. If you've studied and analyzed even some of these you wouldn't be asking internet strangers how to write a fugue theme.
I could say your subject is too short but Bach wrote a lengthy fugue in C major on a theme of just two bars. It starts at 4:29 of this video.https://www.youtube.com/watch?v=nvVFRo_4b0o
BTW, this fugue uses just about every device in fugal writing, inversion, stretto, inversion and stretto simulatneously and then the pedal comes in with augmentation and all three happen simultaneously. This is old Bach at his best.
The important aspect of a fugue theme is that it must be recognizable and memorable. I didn't quite get the rhythm of your theme, but if I was using your notes it would be quarter, quarter, dotted quarter, eighth, eighth, eighth, eighth, eighth, land in a quarter note low G instead of c, then quarter rest. BUT, that's probably just the first phrase. Have you analyzed fugue subjects and their fugues? You say you know counterpoint, that's a good starting point. If I was you I'd start with writing a fugal exposition, it's a smaller bite of the apple. Then I'd start working out what could be done with the theme, inversion, stretto, counter subjects/secondary themes, episodic development, augmentation/diminution.