SME/ Small Biz Owners Feeling the Squeeze?

Have been successfully running a small and medium enterprise for a decade and a half..in the last year or so have found more and more larger corporations squeezing us out of margins and delaying our payments beyond belief..it almost feels that business's must be owned or controlled by this large corporations..owned by the handful of people. Any one else feel this? Or any suggestions what we could be doing better!