Hip pain 19 weeks

Oh, that "loose" feeling sounds like it could be the relaxin hormone doing its thing, very common around this stage but the instability you're describing (feeling like your leg might give way) is a bit more than just general aching, so I'd honestly push to see a women's health physio sooner rather than later rather than just managing it yourself. My friend saw one during her second trimester and said they gave her specific strengthening exercises for the hip stabilisers that made a real difference, rather than just generic stretches. In the meantime, some things that seem to help many mums are seated piriformis stretches (you cross the sore leg over, sit tall, and gently lean forward), sleeping on your side with a pillow between your knees to keep your hips aligned, and warm compresses on the hip for short-term relief, walking is good in principle but if the joint feels unstable, it may be worth dialling back the distance until things are more supported. Do check with your OB or a physio though, especially since you mentioned the locking issue, that really warrants a proper assessment.