I'm Getting Too Old for This

None of my pregnancies have been what anyone would call easy but at the same time they haven't been hard. Yes, I have morning sickness the entire time (threw up yet again this morning) and yes, I'm tired and yes, I get huge and uncomfortable but it's never seemed all that bad. And, despite those annoyances, I have always really enjoyed pregnancy. This time around I'm still enjoying it but I'll admit it's been harder on my body and far more tiring than I ever could have imagined. Is that because I'm pregnant, have two young kids, work full-time and have the residual worry about losing another baby or is it simply because I'm 39? Either way, I'm either getting too old for this or I've got too much else going on for this.