You can get a spring wire rodding tool from a DIY place (a coat hanger is a cheap alternative)
If that meets no resistance then it's further down the soil pipe, follow it down until you find the rodding cover, unscrew that and have a poke about. Flush again to see if it's backing up in that area or further down.
Next step is the outside manhole cover, open it and check the water flow after flushing.
Usually a poke with a stick will undo most blockages, it's just finding the right place first.
Unless you have a skin lesion then you won't catch anything from a toilet.