Help me figure this problem out: I feel unable to be creative and it is making me anxious.
The inability to express one's creativity can indeed cause much anxiety!  One way of looking at your situation could be that you have certain expectations on what counts as being creative, or how the expression should come about—and these expectations might just set a bar too high for yourself.  Could you consider letting go some of them?

Other times we are our own worst critic, instantly dismissing any ideas as not good enough before even putting them into action.  Would it help if you allowed yourself to explore possibilities freely without fear of judgement first?  You don't need to share anything with others unless you think it's worth it!

Another possibility is simply that you find yourself stuck somewhere you didn't plan to get, unsure where to move forward from here.  Have you considered asking someone else (or perhaps me!) to give feedback? Sometimes all it takes is a nudge in the right direction.

Let me know if there was something specific you had in mind when describing your struggle!
I can usually come up with ideas but I never feel that any of them are good enough to continue working on.  Is there any way to help get past this roadblock?
Staying motivated during creative projects is hard, hence why the term writer's block exists. You're not the only one!

Try doing shorter and simpler projects! It's important to finish some projects so you can feel that sweet sense of accomplishment and build up a habit of being creative! 

Having finished projects also make it easier to reflect on what you could do better, and potentially allow you to market yourself better.

Getting other people involved can help inspire you, particularly if they're interested in the medium and can provide good feedback.

Also keep in mind that execution often matters more than the starting idea, so don't worry too much if your idea seems lackluster to you in hindsight.
Please help me come up with some ideas