I have a question about sex

So iv only had two sexual partners and they were both on the smaller side. No big deal you find things you like and it works but with both guys they have had problems keeping it up. My new guy had a hard time the first time we met and had sex and then the second time was a little better and the third time I went down on him and it was a lot better. My problem is we tried to have sex two days in a row and he had a hard time again. I’m not mad or upset I know it happens but I’m starting to think it’s me. I’m on the bigger side weight wise and I feel like he’s not attracted to me. When your in a new relationship isn’t sex supposed to happen a lot and you want to do it all of the time? He couldn’t even do it two days in a row and I’m having a hard time feeling insecure and like it’s me. Is this normal? Does it have to do with size? I’m not very experienced so I don’t know these things. We’ve talked about it and he said it’s not me and he just needs a few days in between to make him last but I feel like that’s not normal I feel like this is new and exciting and he shouldn’t have a problem but like I said I’m not really sure so can someone tell me if it’s normal? Is it me? Feeling real insecure here ☹️