Sorry to hear that you are struggling with your confidence and it sounds like lessons would be a really good start.
I am similar in that I got back into riding and have had a hard time controlling my fears despite having an older well-broke horse who for the most part is pretty well behaved. Some days I have rides that make me think of throwing in the towel but then I will have rides where I can see glimpses of the confident teen rider I used to be.
For instance yesterday I had a very exhausting ride where my horse threw a number of tantrums including suddenly dropping for a roll with me on his back
We then went through a fit of side-stepping and little rears when I wouldn't let him catch up with his mates. I managed to over-come the urge to jump off and lead him and felt really proud of myself for staying on.
Definitely don't push yourself and only do what you feel comfortable, I find reminding myself that it is meant to be FUN and that if I do decide to stop riding it wont be the end of the world helps put things in perspective. I always end up coming back to the fact that although I don't always love riding I love having horses in my life.