Glad it's got better.
Over the first couple of days it is totally normal for a wound to swell up and be painful. I imagine that is what you saw and if the swelling was over certain muscles then it can hurt to move your arm in the direction that requires those to contract as it pulls the skin and the same with if you're trying to put pressure on the muscle by lifting something as well as lifting can put pressure on the skin and try and pull it further open.
Really, if this happens again what you need to look for is whether the pain is there all the time, even if not as bad all the time but aching. If the pain feels like an electric shock. Or if you lose movement and or sensation in any of the areas around or below it. Those are signs that it really needs to be checked as a muscle and/or a nerve may be damaged. The same as if it is down to fat/ gaping more than 1cm, gaping at all on your face/ hands/ near a joint, is bleeding for longer than 10mins under direct, constant pressure/ the blood is really quick or it is pulsing out. If this occurs then you need to go to A&E straight away; if blood is running out really quickly or pulsing then 999.