Taxing
Difficult, testing, exacting, hard, burdensome, formidable, tiring, exhausting, wearisome, uphill, gruelling, Herculean, a tall order, toilsome, challenging, taxing, tough, onerous, stressful, arduous, wearing, wearying, draining, rigorous, back-breaking, punishing, and knackering.
Importunate
Nagging, importunate, possessive, tiresome, exigent, clamorous, insistent, trying, and hard to please.