Please help me resolve my Opperating System (I Think ?) problem

I have an older MacBook Pro 13-inch early 2011, Processor 2.3 GHz Intel Core i5, Memory 4 GB 1333 MHz DDR3, Graphics Intel HD 3000 384 MB. Recently my computer began to slow down and just act off so i took it to a SoCalled 'MacGuy' a friend of my moms who had a computer shop nearby. I say 'had' because he is now a ghost, and the windows of his shop are covered in newspaper and the shop is no more. Anyway I took my old girl to his shop where he informed me my extensive photo library ( which I value more than you could imagine, well thats dramatic I'm sure you can imagine ) was taking up too much space on my hard drive and was slowing my computer down. Sounded reasonable so he said he would get an external drive to store my photos on and her clean up a bit. When i returned to pick her up he had the external hard drive but would not transfer the photo library because it would take too long and I could do it myself no problem once i got home, he also informed me he had installed a new operating system macOS High Sierra 10.13.3.which i had never asked for and also found out that my ever sweet mom had stopped by and paid my bill which was around $400. Needless to say I was slightly upset, well the saga continues. I think I was able to transfer my photo library to the external drive but I'm not positive because there are all these different libraries on my desktop and I'm afraid to delete them for fear of losing photos of deceased love ones and beautiful children. Ok so heres the major problem the computer ran fine for about a day then the operating system did an update since that day my computer is a snail and virtually has become a paper weight. I spent over a week on the phone with multiple different MacSupport agents 5 or 6 who tried (some harder than others) to help me only to be mysteriously disconnected and never called back. Now it takes 3 minutes to open a application from my tool bar and my girl is a hollow shell of her former self. I recently purchased an iPhone X 256Gb and subscribed to apple music which I love BTW !!!!! Alas it's working great on my phone but is nowhere to be found non my MacBook Pro. I OPENLY ADMITT I'M NOT A COMPUTER EXPERT BUT I'M A LOYAL TO THE BONE MACINTOSH USER. Growing up in Woodside Hills, Ca. it was never even a choice to use anything but a Mac. I beg for any help that anyone would or could lend to a very sad person and his paperweight. Mahalo's. JOHNNY U.