Question about Fin

[J15]

Hey guys I just started my fifth month and I had a question about side effects. I was just wondering if it was possible to get side effects only some of the time. Here's what I mean. During my first month I got no sides, second month I was fine half way through but then I lost everything but then it went away. Sometimes I get rock hard erections and sometimes nothing I'm trying to determine if this is because of fin or another injury. I'm confused lol it's like a cycle there has been times after the 3rd month where I took fin and my erections were really hard. It's a cycle I dunno if this is because I might have a muscle injury I'm just trying to determine the source

I'd appreciate the feedback.
Thanks