Sore Inflamed Pec

Well I'm 18 years old and just getting back into lifting after about 7 months.  I lifted on Monday and did 2 sets of 15 reps benching on a smith machine because the gym does not have a free weight bench.  On Tuesday my chest was a little sore and I noticed my right pec was a little larger than my left.  Yesterday I noticed the same thing except my right pec was a little bit larger than the day before.  I also have noticed the size difference today and on all of the days after the lift I have felt the normal soreness (atleast I think it is normal from what I remember about next day soreness).  I am just wondering if I could have possibly strained or torn something in my pec because I don't remember ever getting swelling the day after lifting.  Any help is appreciated!