ASP. NET checkbox onchange

I have a page displaying a table of data pulled from a database. The data is filtered to show the last 6 months of data. I want to put a check box on the page where the user can click on the checkbox to toggle between seeing all the data from all time, to the filtered last 6 months of data. Heres what I have so far:

HTML:

<input type="checkbox" name="datefilter" class="form-check-input" onChange="this.form.submit()">
Display All Time Data

Controller:

    public ActionResult Index(string[] datefilter, string SearchString, string sortOrder, int? page)
    {
        DateTime testDate = DateTime.Now.AddMonths(-3);
        var PatientID = from p in db.PatientTbls
                        select p;
        if (datefilter == null)
        {
            PatientID = PatientID.Where(s => s.CreationDate >= testDate);
        }
        PatientID = PatientID.OrderByDescending(s => s.CreationDate);
        if (!String.IsNullOrEmpty(SearchString))
        {
            PatientID = PatientID.Where(s => s.ReadOnModel.Contains(SearchString) || s.ToBeMarkedOnLaser.Contains(SearchString) || s.Brand.Contains(SearchString));
        }
        return View(PatientID.ToList().ToPagedList(page ?? 1, 150));
    }

My thought was to have the checkbox re-submit the form with the new checked value and the "if" statement would then filter or not filter the results. The issue is when I check the box, it refreshes the page which then clears the checkbox. Also once I check the box once, it forever does not run the date filter query. Any help would be great.

PS. I'm new to all this so please bear with me.

Thanks