Why is my dog arching its back looking uncomfortable?

I have a boy dog getting mounted by my female dog she keeps licking his ear i cant tell if she's doing anything else like hurting him. Last nite he was screaming and started arching his back and looked scared and in pain. Can someone Please help.

It would be better to seperate them for awhile, she's obviously trying to be alpha and bullying him. Which is why it would be best to give him a break from her, remember to scold her when she does this to him. My grandmothers female border collie often does this with my male black labrador. She's trying to teach him she's the boss

You need to get him to a vet. Has he shown any of these symptoms:Attempts to vomit (usually unsuccessful); may occur every 5-30 minutes This seems to be one of the most common symptoms & has been referred to as the "hallmark symptom""Unsuccessful vomiting" means either nothing comes up or possibly just foam and/or mucous comes up Some reports say that it can sound like a repeated cough New Doesn't act like usual self Perhaps the earliest warning sign and may be the only sign that almost always occursWe've had several reports that dogs who bloated asked to go outside in the middle of the night. If this is combined with frequent attempts to vomit, and if your dog doesn't typically ask to go outside in the middle of the night, bloat is a very real possibility. Significant anxiety and restlessnessOne of the earliest warning signs and seems fairly typical"Hunched up" or "roached up" appearanceThis seems to occur fairly frequentlyLack of normal gurgling and digestive sounds in the tummy Many dog owners report this after putting their ear to their dog's tummy.If your dog shows any bloat symptoms, you may want to try this immediately. Bloated abdomen that may feel tight (like a drum)Despite the term "bloat," many times this symptom never occurs or is not apparentPale or off-color gumsDark red in early stages, white or blue in later stagesCoughingUnproductive gaggingHeavy salivating or droolingFoamy mucous around the lips, or vomiting foamy mucousUnproductive attempts to defecateWhiningPacingLicking the airSeeking a hiding placeLooking at their side or other evidence of abdominal pain or discomfortMay refuse to lie down or even sit downMay stand spread-leggedMay curl up in a ball or go into a praying or crouched positionMay attempt to eat small stones and twigsDrinking excessivelyHeavy or rapid pantingShallow breathingCold mouth membranesApparent weakness; unable to stand or has a spread-legged stanceEspecially in advanced stageAccelerated heartbeatHeart rate increases as bloating progressesWeak pulseCollapseIf yes he might have GDV or Bloat, which is deadly.