I've been on antidepressants for more than a decade before my ADHD was diagnosed. They will not solve the problem but they WILL help, if it is the right medication for you. I'd recommend to take the prescribed medication and test for yourself how well you respond to it. For me, antidepressants have been a lifesaver, but getting the right one for your needs and the right dosage is key. Most of all: don't be afraid. There is no need to. Trust your doctor and also your instincts, and clearly communicate should you feel effects you deem to be negative, then work together to find a fitting replacement. There are a great many different SSRIs, at least one of them will be the right choice for you. It can carry you through the hard times, until the fitting ADHD medication can be determined for you.
I was diagnosed - by sheer chance - in May this year. Working together with my doctors, we found Elvanse 60mg for me. And since then my antidepressants could be tapered off completely. Which I'm very happy about - but also aware and grateful. Without the SSRI medication, there is a high chance I wouldn't have lived to have seen the real cause for my depression diagnosed.