Most sheep are seasonal breeders, unless there are a certain percentage of sheep in a flock that are not eg Dorsets when they tend to somehow copy, they do not start to cycle until the day length significantly shortens. Personally speaking having bred both sheep and goats over more than 30 odd years, unless the ram lambs/male kids were late born eg June/July I would think the likelihood of them being fertile not high until over 4 months or so, late borns being a grey area. Also lactation in seasonal breeding animals tends to prevent conception due to the hormones in the body. This is not always so in non seasonal breeding animals such as cattle. So on balance I'd say it was unlikely a 2 month old ram lamb, born in spring to a seasonally breeding type of sheep would cover its mother.