I took a claritin (loratadine) last night and it didn't help at all. i am severely congested and 19 weeks pregnant. can i take zyrtec or allegra now or wait?

Neither would help: Oral antihistamines do not provide decongestion so it would not have mattered. You may try a nasal steroid but there is only one which is considered category B for pregnancy and requires a Rx. Do note that you may also have vasomotor rhinitis associated with pregnancy and this may or may not respond to the usual medications. See doctor .