Yellowing leaves on bottom of vine

Hi all, new here. Love the site...anyway. I have one passion vine I purchased a couple months ago. It is in a large wooden pot with great drainage. My mom said not to overwater it, so I have been very careful not to. However, after having around 10 blooms a day for weeks, now I have none. The leaves at the bottom of the vine are turning yellow and falling off and growth has slowed. It's a purple variety, (sorry new here) and I am not sure of the name. Am I under watering? It sits mostly in the shade and has a trellis to climb on. I sure don't want it to die. Only the bottom of the vine seems to be affected.
Here is a pic of it. And any id info will be appreciated.
Thanks!

~~Peace~~

Looks like P. Amethyst. The yellow leaves could be due to lack of sunlight, increasing temperatures, lack of iron, or lack of fertilizer. And a few yellow leaves are not usually cause for concern if the rest of the plant looks well. You dont say how often you are watering, but you can check the moisture of the soil by sticking your finger in the soil a few inches. If you have warm temperatures, it is okay to water it heavily once every 10 days or so, cause you dont want a sphaghum based potting mix to dry out too much (if thats what you used--they can be hard to "re-wet" if they dry out completely). Mulch can prevent evaporative loss from the surface of the soil--I use the bark mulch. You didnt say if you repotted it when you purchased it, or what kind of potting soil you used. But if you did repot it 2 months ago into standard potting mix, I doubt it needs fertilizer. I wouldn't fertilize until new shoots have stopped growing or almost stopped growing. Then use a slow release balanced fertilizer like Dynamite at half strength. If your local garden centers dont have Dynamite you can get it on Ebay (its the home version of Nutricote, 13-13-13). It takes 2 to 3 weeks to kick in, but works well. Sometimes passies go through phases where they bloom heavily, and then rest for a few weeks. I dont have this one, so I cant speak from experience about it.

Good luck!

Awesome ty Mark. I moved it over about 2 and a half feet. So now instead of being under my back porch awning it is getting morning and mid-day sun. I replanted it from about a 14 inch pot to a big wooden half barrel type pot when I got it.; I used miracle grow soil that feeds. I was only lightly watering it every few days. I did as you suggested and checked the soil. It was quite dry. So I gave it a nice watering, and I just happen to have a bag of bark mulch outside.. I'll give it a layer..Thanks again!