Possible Thyroid Problem

I went to the doctors last week because I have a goitre. I have had a phone call today saying all my tests are normal so I have to go back in to find out what is next. I suspect it will be an ultrasound. I was expecting the problem was due to a lack of iodine but I asked them to test for it, but maybe they didn't. I have been looking into soya milk and the web claims that this can lead to thyroid problems too, but the evidence isn't amazingly conclusive. I'm wondering whether to swap to rice milk, almond milk or oat milk, but they are all extrememly expensive and I'm unsure if they have similar problems. I am worried about the long term affects of a large soya based diet will have on my kids. Any suggestions?