Hey. Yes you can use just one website to promote multiple affiliate programs, but I’d say that your website should focus on just one niche. So you mention, SellHealth, that would lead me to believe your site is about health and fitness. I would then advise you to stick to that niche rather than promoting unrelated products like dog leashes and fashion accessories.
Once you’ve set up your account, do note that Amazon requires you to use product links and generate income from at least three of them within 180 days. If you fail to do so within that time, they will close your account. If you are able to satisfy that requirement, Amazon will review your account as well as your usage of affiliate links once the first sale is complete.