Lost Gallery &Google photos

I'm sorry ,I know that I have seen something about this before .Somehow all my pretty recent pictures from my "camera" section in my gallery,& in my google photos are missing .I think I may have "cleaned " them & somehow lost them,and I really need to know if I can get them back .I still have them in carousel by Dropbox & probably there too , but I didn't check .Someone please tell me if I can do anything about it .I have ccleaner & es task manager, btw. And my phone is a Samsung Galaxy S3 SGH-T999 , T-Mobile but on MetroPcs .thanks.

I have them backed up in Dropbox and Carousel, but wanted to know how, if possible ,I could get them back into the Gallery and/or Google photos. Oh ,and they're also backed up in my laptop too.

— modified on Dec 3, 2015, 4:59:16 PM

So,I just plug in the USB cable from my phone to my laptop ,and I can download the missing pictures back into my phone ? I'm not totally Tech savvy when it comes to certain things , so I just need clarification that this is going to work .Thanks