ESS bitch weeing problems

hope someone can offer advise, my 15mth rescue ess Macey, who we've had since Nov last year, has over the past 3 weeks started weeing when I stroke her and it's not a springer sprinkle, more like a springer flood ! She wags her tail like crazy, rolls on to her back, tail still wagging and it goes every where ! She is neutered, Any ideas as to why she's like that and how can I stop / mimimise it ? Could it be a reaction to my foster, he's been with me since Jan but this is a recent developement ? It appears to me that it's not excitement loke she's scared but she hasn't had anything bad happen to her from me. TIA