Ok my boyfriend and i have been together for a long hard 11 months and happier then ever...but we havin a prob?

im 16 & hes 17...We have and stuff like that but lately hes been having a problem staying hard.. im trying to stop myself from thinking that i just might not be attractive enough for him and hes afraid to tell me..(im a lil on the chubby side) but im also thinking that mabey its because of this lil rash that he got around hiz . it hurts him alot, he could hardly walk sometimes so mabey it hurts him while where in the "act"... ive asked him wuts wrong but he says he honestly has no idea...can sum1 tell me in thier opinion wut the problem might be?? im not asking for sum1 to tell me that im too young to be having . i know this already...and to be honest imma keep on doing it cause i love him..i just wanna know what could be the problom thats makin hiz manhood fall alseep so fast....thanx a bunch...-Alina