～せいか — Perhaps Because Of

年のせいか、最近疲れやすい。

Toshi no sei ka, saikin tsukareyasui.

Maybe because of my age, I get tired easily these days.

Noun 年 + の + せいか tentatively offers age as the possible cause.

緊張していたせいか、うまく話せなかった。

Kinchou shite ita sei ka, umaku hanasenakatta.

Perhaps because I was nervous, I couldn't speak well.

Verb past 緊張していた + せいか suggests nervousness as an uncertain reason.

天気が悪いせいか、客が少ない。

Tenki ga warui sei ka, kyaku ga sukunai.

Maybe because the weather is bad, there are few customers.

い-adj 悪い + せいか speculates that bad weather is behind the low turnout.