After I read the answer of Mrs. Marija and again read your title and question detaily, I would like to make detailed my answer. First, yes different sampling methods can be an obstacle to compare. The most important point about sampling is if this two samples are collected randomly or not. I understand that both sample is collected from Patients. That is good. And one is randomly collected. The other sample is questioned like male or female and age is also questioned interval. This is about your questionnaire and a little bit about your scales. But the question type you used is NOT about your sampling method. If you receive the answers from the population randomly as you did in the first sample, you can compare the data.

In that case, you can compare both samples but size of these samples should be equal or near and also should measure the same variables. And yes again, the best way for you is to get an assistance from someone who has enough knowledge about Statistics. Because Without seeing the data it is NOT posible to guide you. I just make an assumption to give you an answer without seeing data and discussing it. I suggest you to find someone qualified about statistics from your city.

I suppose you should pay attention for random factors and other deviations that might take place in your research. During the 1st review use method of means or median

I'm afraid that you cannot compare the data from these two samples....

The research sample design criteria should be the same, at least, when the respondents are different.

You can describe the findings from both surveys, but only as secondary data analysis.