Aching pain in butt, could I have sciatica?

Piriformis or SIJ. Are also common causes. Piriformis is a muscle that frequently spasms with improper sitting positions or pelvic imbalance. Sij stands for sacroiliac joint which may become dysfunctional for the above reasons.
Yes. When is nerve is mildly irritated, it can manifest as pain in the buttock area. As the irritation becomes more severe, the pain begins to radiate down the leg. The more severe the irritation, the lower into the leg it goes.
NO! Butt pain is not sciatica. Sciatica is when the pain goes all the way into your leg following a particular nerve root distribution. "butt" pain is usually referred from the mechanics of the lumbar spine and usually soft-tissue related (muscle, tendon, ligament). Good back stretching exercises, anti-inflammatory meds, phyical therapy, are all great tools to deal with butt pain.
Spine Pain Options. This chronic pain in the distribution as you suggested is the result of an irritated nerve or facet joints or other injury typically in the lumbar spine (low back) which are caused by herniated disks, spinal stenosis or degenerative disc disease, etc requiring further evaluation by a spine specialist and may be candidate for facet injections/radiofrequency ablation and epidural steroid injection.