Hopefully the OP has addressed the problems as the dog will now be over a year old now.
FWIW, the way I handled leash walking with our now 4 month old puppy started at 8 weeks by having her follow me close with a treat at my side. That morphed into very short walks in the street with the same tactic and a leash on a flat collar. Any time she pulled out ahead or off to the side, I changed directions. With much patience and much praise, that turned into a 4 month old pup that will walk on a loose lead almost at a heel position. I also introduced the "leave it" command so the dog walks and I don't allow random sniffing. When we're walking, we walk. She goes before we start our walk at the house (hurry up command was used since 8 weeks for doing her business). When I eventually introduce heel soon, it will be a piece of cake. I started heavily with treats, and have weaned them off for most of this other than using them periodically for the watch me command while we're walking. That gets her back where I want her by my knee.
That's not to say she doesn't have her moments of lack of control and lack of attention to me. That varies so much with conditions and distractions. We started only on the road as grass has too many smells. Even a wet road changes the picture completely as there are many more smells. Then we worked toward sidewalks, then grassy areas. Then we worked going by adults, kids, other dogs, cars, trucks etc.
It's now time to introduce a choke collar as she is getting big enough, and needs to know there are consequences for not paying attention. Eventually we'll work to off lead stuff and things will get fun.
The OP's dog was already 5 months so much of this early opportunity might have been lost. I've also trained dogs around that age or older, but we started with a choke collar and some treats, and a prong collar, if necessary. Having a dog that doesn't pull (regardless of the collar choice) is way more humane than having one pulling you all over the place. I'm also not a harness fan.