I think my site has been hacked / MySql Injection

Late august, someone informed that in their FF Browser, a plugin detected that the site had a ‘my sql injection’.

earlier today, someone said they played a video / clicked on a post and their norton detected it as a ‘malicious intrusion’

How can i check the site and secure it, without causing more problems.

I also believe one of my email accounts has been hacked (alot of ‘mail return’ from very old contacts), have changed the password again – just a hunch though

and finally, the site in question is renight (dot) com

oh and, I clicked on a link to my site within a Facebook Message and got the adobeflash.org trojan virus automatic download package happen – https://forums.digitalspy.co.uk/showthread.php?t=1553534