Hi Julie,
If you can play the strumming pattern, but then have trouble playing it when you sing the lyrics, then there isn't really a problem in your guitar playing. It is more a problem in your coordination of singing and guitar.

This is pretty common. I think if you work toward getting them both going at the same time, you'll like the results better than if you just let the strumming pattern go.

When I am working on singing a song and playing at the same time, I find I have to practice each separately and both together, and play it enough over and over so it is all from memory. During the beginning I often can't get it all working at the same time and have to "dumb down" the guitar part while I work on coordinating.

So probably not different from your experience. Just don't leave it at that, work toward doing both well at once...eventually.

Hope that helps.

Jon