My son is 14 months old, weighs 22 pounds and I gave him 3.75 ml of tylenol, (acetaminophen) then my husband gave him 3.75 ml right after. What should I do?

Depends . It depends on strength of medicine. Call local poison control number available from your county yellow page . If initial dose was ordered for him does not have other medical conditions and not on other medications may be safe, but call.
Skip next dose. As long as you have not been told to limit your tylenol (acetaminophen) below standard dosing then you are ok. First check to see how much (mg) you gave him. The new children's tylenol (acetaminophen) is 160mg / 5ml(1 teaspoon). If you gave him 3.75ml twice, then you gave him 240mg. The daily max is more important for toxicity. A 22lb child is 10kg. Max daily tylenol (acetaminophen) at that weight is 750mg. So just skip next dose.
No more. As long as it is less than 90 per kg. Your child is 9 so toxic would be 810 in 24 hours. You gave less. Should be ok.
Depends . . . Depends upon concentration of acetaminophen. 100mg/ml, 160mg/5ml or 500mg/15ml. Maximum oral daily dose for infants is 10-15mg/kg/dose every 4-6hrs not to exceed 5 doses in 24yrs (see http://www.Drugs.Com/dosage/acetaminophen.Html). Alternately, infants 8.2-10.8kg who are 1-2yrs old can take 120mg/dose. Depending upon concentration & dose, you may need to take him to er to monitor liver function.