He may not have been socialized well as a baby. Work hard on that! Maybe he is scared. I would do as Sarah suggested and sit on the floor with a treat and call him over to crawl into your lap. Sometimes little puppies are afraid of being lifted way up high.
Godric was this way when I got him as he was not socialized either.
These ladies have given you very good information, I took a slightly different approach because he only did that with me and not my BF so I knew he was testing me so I gave him his space and let him come to me. Once he realized there were sometimes yummies on my desk he was all for it. Now he physically climbs into my lap, he's demanding that way and he's very clingy. If I'm sitting down he's in my lap but at first he was the same.
I think hes playing a game, when we got Diego he was 11 weeks old, and he did this.... he still does it every now and again, so I turn the other way and start walking slowly, he then comes running back and jumps up at my leg.
I forgot to add lotus does this to new people too she gets excited licks then barks and runs away lol but she was/is very well socialised she is just fearful not half as much as she was now I can actually get her to walk down the street with her tail over and she's is getting better in crowds etc
If your dog is nervous you have a very tough time ahead lotus is 5.5 months old (24 weeks) so for 12 weeks I have been taking her to heavily populated areas and making sure she gets to know my family it took a week for her to enjoy going to visit my parents now she bounces like a meercat on speed (pic on back legs lol) when she sees them I've still got a way to go I don't think shell ever be over confident but she will be normal ven if it kills me
So once your dog knows you and is okay with it take him everywhere you'll need to carry him until he's vaccinated but he needs to learn tge world is not scary or you could get a barky snappy chihuahua that were all trying to lose this reputation of!