Newer antihistamines are not anticholinergic. so why are side effects like constipation often reported for claritin (loratadine) for example?

Less cholinergic: The newer "less sedating" llike loratadine and cetirizine still do have some anicholineric effects but much less than the 1st generation ones. I think fexofenadine has the least of the three.

Claritin (loratadine) ?: Constipation must be very very rare with Claritin (loratadine) although it may cause sedation when using higher dose than recommended. If you read the fine prints on side effects re. any pill, you will likely find constipation and diarrhea as one of them even though the incidence may be just 1%- no higher than that from a sugar pill.

Less anticholinergic: Newer generation antihistamines like Claritin (loratadine) still have anticholinergic properties, but to a much lower degree compared with first-gen. Some patients remain highly sensitive to associated side effects.