Ok, so for techniques to try. I tried meditation and I didn't have a lot of luck with it but if it's works for you then by all means, why not! I never really sat in meditation but I did practice a lot of mindfulness in general and I think that will really help you figure out what your thought patterns are.

So to add good things to the lens:
For me, I started purposely noticing what I wanted to see in the world. I chose the topics of gratitude, beauty, humor, self-esteem and excitement. And I kept a journal every night where I forced myself to write a few things I was grateful for, a few things that i felt were beautiful that day, and a few things that were funny. I also wrote down one thing I liked about myself, and one thing I was excited about. It did not feel good at first. It felt stupid and ridiculous. But I kept doing it and within a few weeks it transformed what my mind was looking for. I'd walk in to a place and say "what is beautiful here?" and I'd look at my boyfriend and Id ask myself, "how is he a blessing in my life?" It was so simple but it really worked. Because before that my brain was in the habit of asking questions like "what is scary here?" and "what if he doesn't really love me enough?"

And to erase the negative stuff off your lens:
There is a process of questioning your thoughts called "Inquiry". My favorite teacher is a lady by the name of Byron Katie. She has a worksheet where you take your troublesome thought and question it. And then you turn it around to the other, the self, and to the mind. You ask yourself if you know your thought is true, if you could possibly for sure know that the thought is true. And then you turn it around to see the holes in your logic. You say the opposite of the statement in several different ways.

Also there's a lot of power is just deciding that you don't know. Like, I don't know if I am a success or a failure. I don't know if my job is fulfilling. I don't know if my mother is too emotional. I don't know if the car in front of me is going too slow. There's just not a whole lot that I'm qualified to judge from my very limited perspective of the world. It's super freeing.

As far as your meditation group having those strict spiritual guidelines, I always remember this one quote but I can't remember who said it. The quote is "the hand that points to the moon is not the moon." In my experience, you don't have to do anything to find God. You just have to undo the things that keep you from seeing that you've always been standing in the presence of God.

In all, I would say that anything that makes you suffer is a big giant red flag that your thinking in that area needs questioned.

I hope that helps somehow. And no harm in getting checked out by a doctor.