Packages to model non-linear data?

I already have the curve fitting toolbox for matlab, but I am looking for some type of modeling package that includes more in depth modeling for nonlinear data sets. I've seen the mathematical modeling app and the physical modeling app, but I am unsure if either of those are quite what I need. Just as an example, a typical data set for me would be:

A: 7, 10, 13, 15, 3, 3, 0, 0

B: 8, 12, 9, 9, 2, 2, 1, 0

C: 14, 14, 10, 2, 3, 1, 0, 0

I need to model data sets A,B, and C and contrast essentially the rate of decay between the three. The models I've tried with the curve fitting toolbox through both the custom and suggested equations are not quite suited to fit my data.

I don't have much experience in coding, but MatLab has been a huge help in extracting this data, so I'm hoping I can continue to work with it in the analysis.

Thank you so much for any help or suggestions you may have!