if only vs since

if only

• Even if for no other reason than; only just. 

• Used other than figuratively or idiomatically: see if, only. 

• I wish that; signifies a wish or desire for the present or the future. 

• I wish that; signifies a regret about an action in the past. 

since

• Because. 

• From the time that. 

• At certain points during that period of time. 

• Continuously during that period of time. 

• From a specified time in the past.