What size is your tank? If you find out the name of your fish, it'll help too. I will also note if it is the "kissing fish" I am thinking of, that fish will grow much too big to be in the same tank as your betta. Most plecos get very big and need 80-100 gallons minimum, plus without enough food... They'll start sucking on the slime coat on the fish.
I've seen a 2 inch pleco grow to 9 inches in under a year, be warned
Most importantly right now, are those fish cold water? Tropical? Do you know how big they will get? Compatability is everything... From water temperature, tank size, size of fish etc.