L.I.
Have his tonsils and adenoids looked at when he has his next doctors appointment...We had the same issue in our house and just figured it was just because no two kids are alike that they had such different sleep patterns! Our daughter didn't have strep more often than other kids but we found through a long dramatic battle with the school, that she needed to be seen by an ENT for hearing issues...the hearing issues were nonexsistant when tested at the ENT's office, but he did discover that she had larger adenoids than necessary for her body frame causing her sleep issues. Post surgery, they discovered that she had suffered from chronic tonsilitis for at least 3 years (starting at age 3). So even though we'd had her in for antibiotics every time she had strep and they were looking at her throat each time, they missed looking at the adenoids...
It's just a thought, but maybe your son at 2 1/2 is up and about because his body is telling him that laying down is not comfy....at that age, kids have a hard time knowing WHY and just do....Case in point...our daughter didn't realize what it was like to NOT have a sore throat...she just thought that was how it was suppose to feel....