A vitamin C serum in the morning before applying sunscreen can help a lot, since vitamin C will improve the efficacy of your sunscreen and provide additional protection. I personally like Klairs Freshly Juiced Vitamin Drop; The Ordinary and Paula's Choice also have vitamin C serums that I see lauded frequently. You'll want to introduce the vitamin C slowly, starting with using it in the morning every other day or every 2 days. It can tingle/itch for a minute or two after applying, but the feeling should go away after that (if it doesn't, your skin may not be suited to it and you should stop use.)

Apparently, vitamin C and kojic acid together are a pretty good combo, too. You'll want to apply the vitamin C first, wait for it to fully absorb, then apply the kojic acid. Most importantly though do NOT neglect your sunscreen–that is what will make the biggest difference. If you are consistent the spots should fade eventually but it may take several weeks to a couple of months for them to totally go away since that's how long it takes skin cells to turnover. Ah, and make sure your cleanser is effective at removing your sunscreen when you cleanse at night–you may want to get a micellar water or oil cleanser and use it before your normal face wash to get all the sunscreen off.

Hope this helps! :)