Most sweetening agents be is saccharin/aspartame/acesulfame K/stevia/ neotam etc etc have their own weakness. There is no holy grail in replacement of the golden standard of sucrose/sugar. There are many considerations that you have to take into consideration such as processing requirements (heat/time), local regulation (which is highly regulated), product matrix (diet, half sugar?, minerals?)

Looks like you have overdosed your saccharin. Sacchrin is a very good intense sweetener at certain dosages but its controlled in many countries, some not allowed. ITs relatively cheap as such very much used in certain types of lower cost products such as powder beverages or low cost sodas/energy drinks. Watch if you have minerals like calcium/iron/magnesium, which magnifies the bitter taste.

Aspartame is a good one but its not heat stable and causes bitter taste at the end of the tasting cycle. As such its mostly used in diet beverages in combination with more stable sweeteners such as Ace-K and sucralose.

I personally find that its best to combine regular sucrose with intense sweeteners for best effect. Without background details, cant help much

Higher concentrations of saccharin causes a bitter aftertaste, but combining it with other sweeteners will mask the bitterness. If you look at the labels of sweet products, you can see that sweeteners almost never come alone, but combined. For example, it is common to find aspartame with acesulfame-K, which has a bitter aftertaste similar to that of saccharin.

Also, a news from 2010: 

Researchers have discovered a chemical that specifically blocks people's ability to detect the bitter aftertaste that comes with artificial sweeteners such as saccharin. The key is a molecule known only as GIV3727 that specifically targets and inhibits a handful of human bitter taste receptors, according to a new report.

read it full here 

https://www.sciencedaily.com/releases/2010/05/100527122143.htm