Herb Plant Stems

I'm new to growing herbs. I'm outdoor container gardening. I have several plants that have grown tall yet laid over instead of standing up. I have staked them and they have continued to grow...but they continue to just lay over and some of them have just snapped off. It appears that the stems are not thick and strong. Why is this? I water regularly and I don't water too heavily. I'm using a high quality soil mixture. I have used B1 Thrive Alive. I have added compost to the soil to give nutrients to the plants. I don't know what I'm doing wrong. Also, so many of my plants' leaves are turning yellow or brown. What am I doing wrong? I make sure they have the appropriate required mix of sun and shade.
Thank You

What type of herbs are they?

Sages and Basils die in the Fall. You harvest and dry them and store them.
Oregano, rosemary, thymes, mints, onion chives, parsley, cilantro, dills, leaf celery, fennel, onions, garlic, grow best in our Fall/Winter season and will be starting up now. They will probably die in late July or Aug tho. My oregano is year round.
Parsley is a 2 yr plant, then dies. You did not indicate what herbs you grow, lavendar is touch and go in our heat and humidity. Yellow can be a sign of both too much and too little water. Our sun affects and tells plants what it is time for them to do- low sun and short daylength hours are telling many herbs to slow down. Also with cooler days watering should slow down. Containers especially can hold more water than you think. The dirt in my raised beds is still too hot for some herbs to sprout, but others like the cuke I planted Aug 22nd is producing fruit now- at least til frost.
So, what herbs are you growing?

I don't think Orange has been as dry as this nw side of Houston, but in a drouth leaves drop, my African Blue basil is shedding leaves but still flowering and full of bees. Even if I water many of my soon to die plants are drooping in our heat but they get more sun now than they do in summer, since the sun is different and low to the south.

I'm growing:
Angelica
Arugula
Ashwaghanda
Aztec Sweet Herb
Bacopa
Basil (11 varieties)
Bee Balm (9 varieties)
Giant Catmint
Chamomile (Roman)
Chervil
Chives
Chives (Garlic)
Cilantro
Dill (4 varieties)
Echinacea Purpurea
Epazote
Fennel (Bronze)
Geranium Scented (20 varieties)
Garlic (Elephant)
Ginger
Ginger Cardamom
Gotu Kola
Horseradish
Hyssop (9 varieties)
Lavender (9 varieties)
Lemon Balm
Lemon Leaf
Lemon Verbena
Lemongrass (2 varieties)
Licorice
Lovage
Marigold Scented (4 varieties)
Marjoram Sweet
Mint (12 varieties)
Nasturtium (4 varieties)
Oregano (4 varieties)
Parsley (Italian Flat Leaf)
Patchouli
Passion Flower (Passiflora Incarnata)
Rosemary (8 varieties)
Roseroot
Saffron
Sage (13 varieties)
Scullcap
Self Heal
Sorrel (Garden)
Stevia
Stinging Nettle
Sushni
Sweet Cicely
Sweet Pink
Tarragon (French)
Thyme (4 varieties)
Turmeric
Valerian
Vanilla Grass
Winter Savory

Yeah, you are apt to lose half of those, if the stems turn woody harvest. You have problems with Downy mildew? My sweet basils have fits with it. Is why I grow the African varieties of several herbs- my heat and dryness are terrible this year.
Let me see, yellowing leaves can be both over and under watering. Brown leaves can be pinched dry roots, or too much nitrogen. Many herbs are weeds that thrive on neglect. Pampering them makes them weak, or grow too fast to build strength. Then again, it could simply be Fall die off. Late July and August are considered plant killing months- which means Sept harvests- Cilantro and Arugula will grow fast, harvest fast, replant. I began my Fall planting the end of August for the cooler weather herbs.

An example of Downy Mildew on a Sweet basil. This one is also supposed to have more resistance to that as well, but humid days and no rain are just hard on these. This basil returned to life after August ended. I haven't kept the healthy leaves picked off though. I also have fits with sages in this area sadly. Hope I have helped.

Thank you ALL for all the help. It's much appreciated! Kittriana...thank you for all the detailed info and the pictures for reference. It really helped! No downy mildew yet...but now I know what to look out for...Thanks!
I hope yall don't mind I will probably be asking a lot more questions as I learn all about my new herbs...I have 160 herb plants I have just begun to grow...and with no real base of knowledge...lol. I hope to build this into a business and my goal is to ultimately have a 10 acre herb farm...and a business named "Rosie The Herb Girl".
Thank you...until next time.