On cephalexin 500mg 3/day sulfameth/trimethoprim 800/160 2/day. Can I take these and my Adderall (dextroamphetamine and racemic amphetamine) XR 20 mg? Any interactions between them?

Drug-Drug interacts. There are no reported interactions between these antibiotics and adderall (dextroamphetamine and racemic amphetamine).
Drug interactions. You can use a drug interaction checker whenever you have questions about drug-drug interactions or drug - food interactions. Here is one option (Drugs.Com): https://www.drugs.com/drug_interactions.php Your pharmacist is also an excellent source of information.