Hi Linda,
When I first started my business and it came time for invoicing, I would cringe b/c I generally did not like asking people for money - although I had already rendered services.
Even now, depending on the client (if they're especially good clients), I have trouble invoicing.
What I discovered was it was my views of money and my relationship with it.
It has nothing to do with how you value your services or your time - it has everything to do with how you feel about accepting money from other people.
If you're especially proud, or don't like receiving handouts (how easy is it for you to ask for help when you need it?), then invoicing will most likely be a problem.
Sure, you're not asking your clients for a handout - but it may *seem* that way subconsciously.
That was something I needed to work through before I could see a profit with my web design business.
Remind yourself - you are a business, your time and expertise is your product, and you deserve to be fairly compensated for it - it is not a hand out.
If it's still too difficult, you may want to hire a company or an assistant who will do the invoicing for you - just send them the client information, the totals to bill, and let them collect the money.
And glad to hear you finally got it done - next time, don't wait so long
~ Teli