Subdomains and SEO

Do subdomains have any negative impact on SEO? I have two websites, one is a subdomain of the other main domain. Godaddy is stupid and for some reason made my 2nd website a subdomain of the other. I have been working on posting, building SEO, and posting off targeted keywords, but it feels like I am beating a dead horse. I have not seen any SEO improvement over months. Any guidance? Thanks!

Nope, they don't have a negative impact, unless you spam them to death.

interlink them from your main domain and you should be fine,
are you sure you're targeting the right keywords tho?
posting without any links works only for low competitive keywords, so you might need some links in your case

I personally don't like to use them. I had the same experience as you multiple times.

Either separate domain altogether or /sub-folder.

Is it even indexed and index-able?